4 - AAT 'morx' implementation.
6 - Return "safe-to-break" bit from shaping.
8 - Implement 'rand' feature.
10 - mask propagation? (when ligation, "or" the masks).
16 - API to accept a list of languages?
18 - Add init_func to font_funcs. Adjust ft.
20 - 'const' for getter APIs? (use mutable internally)
22 - Remove hb_ot_shape_glyphs_closure()?
28 - Language to/from script.
34 - Add sanitize API (and a cached version, that saves result on blob user-data)
36 - BCP 47 language handling / API (language_matches?)
38 - Add hb_font_create_unscaled()?
40 - Add query / enumeration API for aalt-like features?
42 - SFNT api? get_num_faces? get_table_tags? (there's something in stash)
44 - Add segmentation API
46 - Add hb-fribidi glue?
49 hb-view / hb-shape enhancements:
50 ===============================
52 - Add --width, --height, --auto-size, --ink-box, --align, etc?
58 - ot-layout enumeration API (needs font)
60 - Finish test-shape.c, grep for TODO
62 - Finish test-unicode.c, grep for TODO
64 - GObject, FreeType, etc
66 - hb_cache_t and relatives
68 - hb_feature_to/from_string
69 - hb_buffer_[sg]et_contents