Changes 0.9.20:

General:
- Misc substitute_closure() fixes.
- Build fixes.

Documentation:
- gtk-doc boilerplate integrated.  Docs are built now, but
  contain no contents.  By next release hopefully we have
  some content in.  Enable using --enable-gtk-doc.

GObject and Introspection:
- Added harfbuzz-gobject library (hb-gobject.h) that has type
  bindings for all HarfBuzz objects and enums.  Enable using
  --with-gobject.
- Added gobject-introspection boilerplate.  Nothing useful
  right now.  Work in progress.  Gets enabled automatically if
  --with-gobject is used.  Override with --disable-introspection.

OpenType shaper:
- Apply 'mark' in Myanmar shaper.
- Don't apply 'dlig' by default.

Uniscribe shaper:
- Support user features.
- Fix loading of fonts that are also installed on the system.
- Fix shaping of Arabic Presentation Forms.
- Fix build with wide chars.

CoreText shaper:
- Support user features.

Source changes:
- hb_face_t code moved to hb-face.h / hb-face.cc.
- Added hb-deprecated.h.

API changes:
- Added HB_DISABLE_DEPRECATED.
- Deprecated HB_SCRIPT_CANADIAN_ABORIGINAL; replaced by
  HB_SCRIPT_CANADIAN_SYLLABICS.
- Deprecated HB_BUFFER_FLAGS_DEFAULT; replaced by
  HB_BUFFER_FLAG_DEFAULT.
- Deprecated HB_BUFFER_SERIALIZE_FLAGS_DEFAULT; replaced by
  HB_BUFFER_SERIALIZE_FLAG_DEFAULT.

(adam)