----------------------------
- [featureVars] Allow to register the same set of substitution rules to multiple features.
The ``addFeatureVariations`` function can now take a list of featureTags; similarly, the
lib key 'com.github.fonttools.varLib.featureVarsFeatureTag' can now take a
comma-separateed string of feature tags (e.g. "salt,ss01") instead of a single tag (3360).
- [featureVars] Don't overwrite GSUB FeatureVariations, but append new records to it
for features which are not already there. But raise ``VarLibError`` if the feature tag
already has feature variations associated with it (3363).
- [varLib] Added ``addGSUBFeatureVariations`` function to add GSUB Feature Variations
to an existing variable font from rules defined in a DesignSpace document (3362).
- [varLib.interpolatable] Various bugfixes and rendering improvements. In particular,
a new test for "underweight" glyphs. The new test reports quite a few false-positives
though. Please send feedback.