Ufo2ft

- [API] Added compileVariableTTF and compileVariableCFF2 public functions (332).
- [kernFeatureWriter] Added Nandinagari to list of "Indic" scripts (331).
- [preProcessor] Load custom filters in TTFInterpolatablePreProcessor (333).
- Bumped minimum required fonttools >= 3.42.0

- [API] Added compileVariableTTF and compileVariableCFF2 public functions (332).
- [kernFeatureWriter] Added Nandinagari to list of "Indic" scripts (331).
- [preProcessor] Load custom filters in TTFInterpolatablePreProcessor (333).

- Implemented `public.skipExportGlyphs` UFO and DesignSpace lib key, for excluding specific glyphs from final binary font (318).
NOTE: The feature file is not subsetted yet. If you reference glyphs that are excluded from export, the feature compiler will crash.
- [propagateAnchors] Correctly propagate anchors for composite glyphs that combine multiple mark glyphs (e.g. "circumflexcomb_tildecomb") (316).
- [decomposeComponents] Fixed duplicate decomposition of nested components in OTFs when using defcon UFO backend (322).
- [kernFeatureWriter] Write separate kern lookup without `lookupflag IgnoreMarks` for the kerning pairs that contain any mark glyphs (314, 328).
- Moved `maxContextCalc` module to `fontTools.otlLib`, but kept a stub that re-imports from the new location, for backward compatibility. This will be removed in the future.

- [outlineCompiler] Only build minimal metrics/outline tables for "sparse" layer masters when compiling interpolatable TTFs or OTFs from designspace sources (310).

- Added ``layerName`` argument (``str``) to ``compileOTF`` and ``compileTTF``, and ``layerNames`` argument (``List[Optional[str]]``) to ``compileInterpolatableTTFs``, for compiling outlines from a different UFO3 layer than the default UFO layer.
Note that OpenType features compilation is skipped when ``layerName`` is given, as it is assumed that the ``features.fea`` only refers to the default UFO layer.
- Added ``compileInterpolatableTTFsFromDS`` and ``compileInterpolatableOTFsFromDS`` functions that take a FontTools' ``DesignSpaceDocument`` object and compile OpenType font masters suitable for generating a variable font. All the ``SourceDescriptor`` objects in the designspace should have their ``font`` attribute set to a pre-loaded ``defcon.Font`` or a compatible UFO Font class. The functions return a copy (or same instance if ``inplace=True``) of the designspace document with the sources' ``font`` attributes set to the respective ``TTFont`` instances. Sources with ``layerName`` attribute (e.g. to define sparse intermediate masters) are also supported: i.e. outlines are converted/compiled compatibly from non-default layers, whereas features are only compiled for
the default layers.
- [cubicToQuadratic] The Cu2Qu ``curve_type`` custom parameter is now stored in the layer's ``lib`` element of ``layerinfo.plist`` instead of in the global ``lib.plist``, as different layers may well have different curve type.
- Fixed incorrect Family and SubFamily nameIDs (1 and 2) that were generated as fallbacks when UFO ``fontinfo.plist`` doesn't explicitly define ``styleMapFamilyName`` and ``styleMapStyleName`` (299).
- Bumped minimum installation requirements:
* fonttools >= 3.35.0
* cu2qu >= 1.6.5
* booleanOperations >= 0.8.2

The ``optimizeCFF`` compile option is no longer a bool, but now takes an integer (or enum) value:
* 0: no optimizations
* 1: charstring operators' specialization only, without subroutinization
* 2 (default): both specialization and subroutinization

Changes in installation requirements:

- fonttools[ufo] >= 3.32.0 (for the `fontTools.ufoLib` module);
Removed standalone 'ufoLib' from requirements.
- defcon >= 0.6.0
- cu2qu >= 1.6.4