- Test OpenType 1.6 mark filtering sets
- HB_OT_LAYOUT_GLYPH_CLASS_BASE_GLYPH vs LookupType::... mess
- remove hb_ot_layout_feature_mask_t in favore of hb_mask_t or something
- Rename LookupFlag::MarkAttachmentType to LookupFlag:IgnoreSpecialMarks
- cmap14 support in get_glyph callback
- size_t?
- change get_XXX_count / get_XXX_tag to be more like
  hb_ot_layout_get_lig_carets (IN/OUT)?
- Figure out compiler selection (add test for link to libstdc++)