Ufo2ft

- Use `cffsubr` by default for both CFF 1.0 and CFF2 (465). Make `compreffor` an optional requirement (464).
- Added support for ` Automatic Code` special marker comments to allow inserting auto-generated features in specific places of the features.fea, similar to Glyphs.app (458, 482, 351).
- Allow to run ufo2ft filters and featureWriters from the command line, which can be helpful for testing purposes (470, 473).
- Added `loadFilterFromString` function, pass `filters` argument to compile functions and PreProcessor (466, 479, googlefonts/fontmake737).
- Added GDEF feature writer (enabled by default) that generates GlyphClassDefs based on UFO public.openTypeCategories, and also generates ligature caret statements based on "caret_" or "vcaret_" named glyph anchors (480).

- [flattenCompontents] Fixed issue with mixed contour+component glyphs in nested components (448).
- [flattenCompontents] Fixed issue with transformed nested components ending up with the wrong translation offset (450).

Added ``flattenComponents`` compile option. If set, composite glyphs with nested components are flattened so that they have at most one level of components (438).

[featureWriters] Fixed `KeyError` when glyphOrder contains more glyphs than the glyphSet subsetted with 'public.skipExportGlyphs' UFO lib key (432, 434).

- Improved VORG table generation: only add vertOriginY if != default (418).
- [markFeatureWriter] Support multiple anchor classes per mark glyph in the mark feature (303, 416).
- [postProcessor] Update `charset` when renaming glyphs in CFF2 table (423).
- [featureWriters] Apply `public.skipExportGlyphs` for standalone feature writers as well (we already did for regular writers that are initialised through the FeatureCompiler) (411).
- Bump minimum fonttools requirement to 4.17.1.