Public headers: Decorate public symbols with HB_EXTERN

This prepares the headers for exporting symbols using visibility
attributes or __declspec(dllexport), so that we do not need to maintain
symbols listing files, as this is what was and is done in GLib and GTK+.
diff --git a/src/hb-font.h b/src/hb-font.h
index fb4a0ea..c3165e1 100644
--- a/src/hb-font.h
+++ b/src/hb-font.h
@@ -46,19 +46,19 @@
 
 typedef struct hb_font_funcs_t hb_font_funcs_t;
 
-hb_font_funcs_t *
+HB_EXTERN hb_font_funcs_t *
 hb_font_funcs_create (void);
 
-hb_font_funcs_t *
+HB_EXTERN hb_font_funcs_t *
 hb_font_funcs_get_empty (void);
 
-hb_font_funcs_t *
+HB_EXTERN hb_font_funcs_t *
 hb_font_funcs_reference (hb_font_funcs_t *ffuncs);
 
-void
+HB_EXTERN void
 hb_font_funcs_destroy (hb_font_funcs_t *ffuncs);
 
-hb_bool_t
+HB_EXTERN hb_bool_t
 hb_font_funcs_set_user_data (hb_font_funcs_t    *ffuncs,
 			     hb_user_data_key_t *key,
 			     void *              data,
@@ -66,15 +66,15 @@
 			     hb_bool_t           replace);
 
 
-void *
+HB_EXTERN void *
 hb_font_funcs_get_user_data (hb_font_funcs_t    *ffuncs,
 			     hb_user_data_key_t *key);
 
 
-void
+HB_EXTERN void
 hb_font_funcs_make_immutable (hb_font_funcs_t *ffuncs);
 
-hb_bool_t
+HB_EXTERN hb_bool_t
 hb_font_funcs_is_immutable (hb_font_funcs_t *ffuncs);
 
 
@@ -151,7 +151,7 @@
  *
  * Since: 0.9.2
  **/
-void
+HB_EXTERN void
 hb_font_funcs_set_glyph_func (hb_font_funcs_t *ffuncs,
 			      hb_font_get_glyph_func_t func,
 			      void *user_data, hb_destroy_func_t destroy);
@@ -167,7 +167,7 @@
  *
  * Since: 0.9.2
  **/
-void
+HB_EXTERN void
 hb_font_funcs_set_glyph_h_advance_func (hb_font_funcs_t *ffuncs,
 					hb_font_get_glyph_h_advance_func_t func,
 					void *user_data, hb_destroy_func_t destroy);
@@ -183,7 +183,7 @@
  *
  * Since: 0.9.2
  **/
-void
+HB_EXTERN void
 hb_font_funcs_set_glyph_v_advance_func (hb_font_funcs_t *ffuncs,
 					hb_font_get_glyph_v_advance_func_t func,
 					void *user_data, hb_destroy_func_t destroy);
@@ -199,7 +199,7 @@
  *
  * Since: 0.9.2
  **/
-void
+HB_EXTERN void
 hb_font_funcs_set_glyph_h_origin_func (hb_font_funcs_t *ffuncs,
 				       hb_font_get_glyph_h_origin_func_t func,
 				       void *user_data, hb_destroy_func_t destroy);
@@ -215,7 +215,7 @@
  *
  * Since: 0.9.2
  **/
-void
+HB_EXTERN void
 hb_font_funcs_set_glyph_v_origin_func (hb_font_funcs_t *ffuncs,
 				       hb_font_get_glyph_v_origin_func_t func,
 				       void *user_data, hb_destroy_func_t destroy);
@@ -231,7 +231,7 @@
  *
  * Since: 0.9.2
  **/
-void
+HB_EXTERN void
 hb_font_funcs_set_glyph_h_kerning_func (hb_font_funcs_t *ffuncs,
 					hb_font_get_glyph_h_kerning_func_t func,
 					void *user_data, hb_destroy_func_t destroy);
@@ -247,7 +247,7 @@
  *
  * Since: 0.9.2
  **/
-void
+HB_EXTERN void
 hb_font_funcs_set_glyph_v_kerning_func (hb_font_funcs_t *ffuncs,
 					hb_font_get_glyph_v_kerning_func_t func,
 					void *user_data, hb_destroy_func_t destroy);
@@ -263,7 +263,7 @@
  *
  * Since: 0.9.2
  **/
-void
+HB_EXTERN void
 hb_font_funcs_set_glyph_extents_func (hb_font_funcs_t *ffuncs,
 				      hb_font_get_glyph_extents_func_t func,
 				      void *user_data, hb_destroy_func_t destroy);
@@ -279,7 +279,7 @@
  *
  * Since: 0.9.2
  **/
-void
+HB_EXTERN void
 hb_font_funcs_set_glyph_contour_point_func (hb_font_funcs_t *ffuncs,
 					    hb_font_get_glyph_contour_point_func_t func,
 					    void *user_data, hb_destroy_func_t destroy);
@@ -295,7 +295,7 @@
  *
  * Since: 0.9.2
  **/
-void
+HB_EXTERN void
 hb_font_funcs_set_glyph_name_func (hb_font_funcs_t *ffuncs,
 				   hb_font_get_glyph_name_func_t func,
 				   void *user_data, hb_destroy_func_t destroy);
@@ -311,7 +311,7 @@
  *
  * Since: 0.9.2
  **/
-void
+HB_EXTERN void
 hb_font_funcs_set_glyph_from_name_func (hb_font_funcs_t *ffuncs,
 					hb_font_get_glyph_from_name_func_t func,
 					void *user_data, hb_destroy_func_t destroy);
@@ -319,49 +319,49 @@
 
 /* func dispatch */
 
-hb_bool_t
+HB_EXTERN hb_bool_t
 hb_font_get_glyph (hb_font_t *font,
 		   hb_codepoint_t unicode, hb_codepoint_t variation_selector,
 		   hb_codepoint_t *glyph);
 
-hb_position_t
+HB_EXTERN hb_position_t
 hb_font_get_glyph_h_advance (hb_font_t *font,
 			     hb_codepoint_t glyph);
-hb_position_t
+HB_EXTERN hb_position_t
 hb_font_get_glyph_v_advance (hb_font_t *font,
 			     hb_codepoint_t glyph);
 
-hb_bool_t
+HB_EXTERN hb_bool_t
 hb_font_get_glyph_h_origin (hb_font_t *font,
 			    hb_codepoint_t glyph,
 			    hb_position_t *x, hb_position_t *y);
-hb_bool_t
+HB_EXTERN hb_bool_t
 hb_font_get_glyph_v_origin (hb_font_t *font,
 			    hb_codepoint_t glyph,
 			    hb_position_t *x, hb_position_t *y);
 
-hb_position_t
+HB_EXTERN hb_position_t
 hb_font_get_glyph_h_kerning (hb_font_t *font,
 			     hb_codepoint_t left_glyph, hb_codepoint_t right_glyph);
-hb_position_t
+HB_EXTERN hb_position_t
 hb_font_get_glyph_v_kerning (hb_font_t *font,
 			     hb_codepoint_t top_glyph, hb_codepoint_t bottom_glyph);
 
-hb_bool_t
+HB_EXTERN hb_bool_t
 hb_font_get_glyph_extents (hb_font_t *font,
 			   hb_codepoint_t glyph,
 			   hb_glyph_extents_t *extents);
 
-hb_bool_t
+HB_EXTERN hb_bool_t
 hb_font_get_glyph_contour_point (hb_font_t *font,
 				 hb_codepoint_t glyph, unsigned int point_index,
 				 hb_position_t *x, hb_position_t *y);
 
-hb_bool_t
+HB_EXTERN hb_bool_t
 hb_font_get_glyph_name (hb_font_t *font,
 			hb_codepoint_t glyph,
 			char *name, unsigned int size);
-hb_bool_t
+HB_EXTERN hb_bool_t
 hb_font_get_glyph_from_name (hb_font_t *font,
 			     const char *name, int len, /* -1 means nul-terminated */
 			     hb_codepoint_t *glyph);
@@ -369,52 +369,52 @@
 
 /* high-level funcs, with fallback */
 
-void
+HB_EXTERN void
 hb_font_get_glyph_advance_for_direction (hb_font_t *font,
 					 hb_codepoint_t glyph,
 					 hb_direction_t direction,
 					 hb_position_t *x, hb_position_t *y);
-void
+HB_EXTERN void
 hb_font_get_glyph_origin_for_direction (hb_font_t *font,
 					hb_codepoint_t glyph,
 					hb_direction_t direction,
 					hb_position_t *x, hb_position_t *y);
-void
+HB_EXTERN void
 hb_font_add_glyph_origin_for_direction (hb_font_t *font,
 					hb_codepoint_t glyph,
 					hb_direction_t direction,
 					hb_position_t *x, hb_position_t *y);
-void
+HB_EXTERN void
 hb_font_subtract_glyph_origin_for_direction (hb_font_t *font,
 					     hb_codepoint_t glyph,
 					     hb_direction_t direction,
 					     hb_position_t *x, hb_position_t *y);
 
-void
+HB_EXTERN void
 hb_font_get_glyph_kerning_for_direction (hb_font_t *font,
 					 hb_codepoint_t first_glyph, hb_codepoint_t second_glyph,
 					 hb_direction_t direction,
 					 hb_position_t *x, hb_position_t *y);
 
-hb_bool_t
+HB_EXTERN hb_bool_t
 hb_font_get_glyph_extents_for_origin (hb_font_t *font,
 				      hb_codepoint_t glyph,
 				      hb_direction_t direction,
 				      hb_glyph_extents_t *extents);
 
-hb_bool_t
+HB_EXTERN hb_bool_t
 hb_font_get_glyph_contour_point_for_origin (hb_font_t *font,
 					    hb_codepoint_t glyph, unsigned int point_index,
 					    hb_direction_t direction,
 					    hb_position_t *x, hb_position_t *y);
 
 /* Generates gidDDD if glyph has no name. */
-void
+HB_EXTERN void
 hb_font_glyph_to_string (hb_font_t *font,
 			 hb_codepoint_t glyph,
 			 char *s, unsigned int size);
 /* Parses gidDDD and uniUUUU strings automatically. */
-hb_bool_t
+HB_EXTERN hb_bool_t
 hb_font_glyph_from_string (hb_font_t *font,
 			   const char *s, int len, /* -1 means nul-terminated */
 			   hb_codepoint_t *glyph);
@@ -426,22 +426,22 @@
 
 /* Fonts are very light-weight objects */
 
-hb_font_t *
+HB_EXTERN hb_font_t *
 hb_font_create (hb_face_t *face);
 
-hb_font_t *
+HB_EXTERN hb_font_t *
 hb_font_create_sub_font (hb_font_t *parent);
 
-hb_font_t *
+HB_EXTERN hb_font_t *
 hb_font_get_empty (void);
 
-hb_font_t *
+HB_EXTERN hb_font_t *
 hb_font_reference (hb_font_t *font);
 
-void
+HB_EXTERN void
 hb_font_destroy (hb_font_t *font);
 
-hb_bool_t
+HB_EXTERN hb_bool_t
 hb_font_set_user_data (hb_font_t          *font,
 		       hb_user_data_key_t *key,
 		       void *              data,
@@ -449,46 +449,46 @@
 		       hb_bool_t           replace);
 
 
-void *
+HB_EXTERN void *
 hb_font_get_user_data (hb_font_t          *font,
 		       hb_user_data_key_t *key);
 
-void
+HB_EXTERN void
 hb_font_make_immutable (hb_font_t *font);
 
-hb_bool_t
+HB_EXTERN hb_bool_t
 hb_font_is_immutable (hb_font_t *font);
 
-void
+HB_EXTERN void
 hb_font_set_parent (hb_font_t *font,
 		    hb_font_t *parent);
 
-hb_font_t *
+HB_EXTERN hb_font_t *
 hb_font_get_parent (hb_font_t *font);
 
-hb_face_t *
+HB_EXTERN hb_face_t *
 hb_font_get_face (hb_font_t *font);
 
 
-void
+HB_EXTERN void
 hb_font_set_funcs (hb_font_t         *font,
 		   hb_font_funcs_t   *klass,
 		   void              *font_data,
 		   hb_destroy_func_t  destroy);
 
 /* Be *very* careful with this function! */
-void
+HB_EXTERN void
 hb_font_set_funcs_data (hb_font_t         *font,
 		        void              *font_data,
 		        hb_destroy_func_t  destroy);
 
 
-void
+HB_EXTERN void
 hb_font_set_scale (hb_font_t *font,
 		   int x_scale,
 		   int y_scale);
 
-void
+HB_EXTERN void
 hb_font_get_scale (hb_font_t *font,
 		   int *x_scale,
 		   int *y_scale);
@@ -496,12 +496,12 @@
 /*
  * A zero value means "no hinting in that direction"
  */
-void
+HB_EXTERN void
 hb_font_set_ppem (hb_font_t *font,
 		  unsigned int x_ppem,
 		  unsigned int y_ppem);
 
-void
+HB_EXTERN void
 hb_font_get_ppem (hb_font_t *font,
 		  unsigned int *x_ppem,
 		  unsigned int *y_ppem);