[API] Remove const from font user_data
diff --git a/src/hb-font.cc b/src/hb-font.cc
index c289f14..a0485a5 100644
--- a/src/hb-font.cc
+++ b/src/hb-font.cc
@@ -43,12 +43,12 @@
 
 static hb_bool_t
 hb_font_get_contour_point_nil (hb_font_t *font HB_UNUSED,
-			       const void *font_data HB_UNUSED,
+			       void *font_data HB_UNUSED,
 			       hb_codepoint_t glyph,
 			       unsigned int point_index,
 			       hb_position_t *x,
 			       hb_position_t *y,
-			       const void *user_data HB_UNUSED)
+			       void *user_data HB_UNUSED)
 {
   if (font->parent) {
     hb_bool_t ret;
@@ -66,11 +66,11 @@
 
 static void
 hb_font_get_glyph_advance_nil (hb_font_t *font HB_UNUSED,
-			       const void *font_data HB_UNUSED,
+			       void *font_data HB_UNUSED,
 			       hb_codepoint_t glyph,
 			       hb_position_t *x_advance,
 			       hb_position_t *y_advance,
-			       const void *user_data HB_UNUSED)
+			       void *user_data HB_UNUSED)
 {
   if (font->parent) {
     hb_font_get_glyph_advance (font->parent, glyph, x_advance, y_advance);
@@ -83,10 +83,10 @@
 
 static void
 hb_font_get_glyph_extents_nil (hb_font_t *font HB_UNUSED,
-			       const void *font_data HB_UNUSED,
+			       void *font_data HB_UNUSED,
 			       hb_codepoint_t glyph,
 			       hb_glyph_extents_t *extents,
-			       const void *user_data HB_UNUSED)
+			       void *user_data HB_UNUSED)
 {
   if (font->parent) {
     hb_font_get_glyph_extents (font->parent, glyph, extents);
@@ -101,10 +101,10 @@
 
 static hb_codepoint_t
 hb_font_get_glyph_nil (hb_font_t *font HB_UNUSED,
-		       const void *font_data HB_UNUSED,
+		       void *font_data HB_UNUSED,
 		       hb_codepoint_t unicode,
 		       hb_codepoint_t variation_selector,
-		       const void *user_data HB_UNUSED)
+		       void *user_data HB_UNUSED)
 {
   if (font->parent)
     return hb_font_get_glyph (font->parent, unicode, variation_selector);
@@ -114,12 +114,12 @@
 
 static void
 hb_font_get_kerning_nil (hb_font_t *font HB_UNUSED,
-			 const void *font_data HB_UNUSED,
+			 void *font_data HB_UNUSED,
 			 hb_codepoint_t first_glyph,
 			 hb_codepoint_t second_glyph,
 			 hb_position_t *x_kern,
 			 hb_position_t *y_kern,
-			 const void *user_data HB_UNUSED)
+			 void *user_data HB_UNUSED)
 {
   if (font->parent) {
     hb_font_get_kerning (font->parent, first_glyph, second_glyph, x_kern, y_kern);
diff --git a/src/hb-font.h b/src/hb-font.h
index 17e7f91..bb53f8f 100644
--- a/src/hb-font.h
+++ b/src/hb-font.h
@@ -128,25 +128,25 @@
 } hb_glyph_extents_t;
 
 
-typedef hb_bool_t (*hb_font_get_contour_point_func_t) (hb_font_t *font, const void *font_data,
+typedef hb_bool_t (*hb_font_get_contour_point_func_t) (hb_font_t *font, void *font_data,
 						       hb_codepoint_t glyph, unsigned int point_index,
 						       hb_position_t *x, hb_position_t *y,
-						       const void *user_data);
-typedef void (*hb_font_get_glyph_advance_func_t) (hb_font_t *font, const void *font_data,
+						       void *user_data);
+typedef void (*hb_font_get_glyph_advance_func_t) (hb_font_t *font, void *font_data,
 						  hb_codepoint_t glyph,
 						  hb_position_t *x_advance, hb_position_t *y_advance,
-						  const void *user_data);
-typedef void (*hb_font_get_glyph_extents_func_t) (hb_font_t *font, const void *font_data,
+						  void *user_data);
+typedef void (*hb_font_get_glyph_extents_func_t) (hb_font_t *font, void *font_data,
 						  hb_codepoint_t glyph,
 						  hb_glyph_extents_t *extents,
-						  const void *user_data);
-typedef hb_codepoint_t (*hb_font_get_glyph_func_t) (hb_font_t *font, const void *font_data,
+						  void *user_data);
+typedef hb_codepoint_t (*hb_font_get_glyph_func_t) (hb_font_t *font, void *font_data,
 						    hb_codepoint_t unicode, hb_codepoint_t variation_selector,
-						    const void *user_data);
-typedef void (*hb_font_get_kerning_func_t) (hb_font_t *font, const void *font_data,
+						    void *user_data);
+typedef void (*hb_font_get_kerning_func_t) (hb_font_t *font, void *font_data,
 					    hb_codepoint_t first_glyph, hb_codepoint_t second_glyph,
 					    hb_position_t *x_kern, hb_position_t *y_kern,
-					    const void *user_data);
+					    void *user_data);
 
 
 void
diff --git a/src/hb-ft.cc b/src/hb-ft.cc
index 3fe2365..a0c7521 100644
--- a/src/hb-ft.cc
+++ b/src/hb-ft.cc
@@ -38,12 +38,12 @@
 
 static hb_bool_t
 hb_ft_get_contour_point (hb_font_t *font HB_UNUSED,
-			 const void *font_data,
+			 void *font_data,
 			 hb_codepoint_t glyph,
 			 unsigned int point_index,
 			 hb_position_t *x,
 			 hb_position_t *y,
-			 const void *user_data HB_UNUSED)
+			 void *user_data HB_UNUSED)
 {
   FT_Face ft_face = (FT_Face) font_data;
   int load_flags = FT_LOAD_DEFAULT;
@@ -67,11 +67,11 @@
 
 static void
 hb_ft_get_glyph_advance (hb_font_t *font HB_UNUSED,
-			 const void *font_data,
+			 void *font_data,
 			 hb_codepoint_t glyph,
 			 hb_position_t *x_advance,
 			 hb_position_t *y_advance,
-			 const void *user_data HB_UNUSED)
+			 void *user_data HB_UNUSED)
 {
   FT_Face ft_face = (FT_Face) font_data;
   int load_flags = FT_LOAD_DEFAULT;
@@ -87,10 +87,10 @@
 
 static void
 hb_ft_get_glyph_extents (hb_font_t *font HB_UNUSED,
-			 const void *font_data,
+			 void *font_data,
 			 hb_codepoint_t glyph,
 			 hb_glyph_extents_t *extents,
-			 const void *user_data HB_UNUSED)
+			 void *user_data HB_UNUSED)
 {
   FT_Face ft_face = (FT_Face) font_data;
   int load_flags = FT_LOAD_DEFAULT;
@@ -109,10 +109,10 @@
 
 static hb_codepoint_t
 hb_ft_get_glyph (hb_font_t *font HB_UNUSED,
-		 const void *font_data,
+		 void *font_data,
 		 hb_codepoint_t unicode,
 		 hb_codepoint_t variation_selector,
-		 const void *user_data HB_UNUSED)
+		 void *user_data HB_UNUSED)
 
 {
   FT_Face ft_face = (FT_Face) font_data;
@@ -130,12 +130,12 @@
 
 static void
 hb_ft_get_kerning (hb_font_t *font HB_UNUSED,
-		   const void *font_data,
+		   void *font_data,
 		   hb_codepoint_t first_glyph,
 		   hb_codepoint_t second_glyph,
 		   hb_position_t *x_kern,
 		   hb_position_t *y_kern,
-		   const void *user_data HB_UNUSED)
+		   void *user_data HB_UNUSED)
 {
   FT_Face ft_face = (FT_Face) font_data;
   FT_Vector kerning;