Add +hb_font_get_glyph_advances_for_direction

New API:
+hb_font_get_glyph_advances_for_direction
diff --git a/src/hb-font.h b/src/hb-font.h
index 37c9a67..cd21153 100644
--- a/src/hb-font.h
+++ b/src/hb-font.h
@@ -529,6 +529,14 @@
 					 hb_direction_t direction,
 					 hb_position_t *x, hb_position_t *y);
 HB_EXTERN void
+hb_font_get_glyph_advances_for_direction (hb_font_t* font,
+					  hb_direction_t direction,
+					  unsigned count,
+					  hb_codepoint_t *first_glyph,
+					  unsigned glyph_stride,
+					  hb_position_t *first_advance,
+					  unsigned advance_stride);
+HB_EXTERN void
 hb_font_get_glyph_origin_for_direction (hb_font_t *font,
 					hb_codepoint_t glyph,
 					hb_direction_t direction,