[API] Add support for vertical text
Design not final yet, and in fact I'm going to change it immediately,
but this is an standalone change for itself.
diff --git a/src/hb-ot-layout-gsubgpos-private.hh b/src/hb-ot-layout-gsubgpos-private.hh
index 422ee43..4d6656a 100644
--- a/src/hb-ot-layout-gsubgpos-private.hh
+++ b/src/hb-ot-layout-gsubgpos-private.hh
@@ -56,6 +56,7 @@
hb_font_t *font;
hb_face_t *face;
hb_buffer_t *buffer;
+ hb_direction_t direction;
hb_mask_t lookup_mask;
unsigned int context_length;
unsigned int nesting_level_left;