* Rewrote the back-end to use the new [fontTools otlLib API](https://fonttools.readthedocs.io/en/latest/otlLib/builder.html#fontTools.otlLib.builder.buildStatTable) for building STAT tables.
* More sanity checks:
* Linked values must be present in the Stylespace (24)
* Location values must be unique (25)
* All Stylespace name records must be available in the default "en" languages (English, United States), the font must contain names for the Windows platform, Unicode BMP encoding, US-American English.
* Additional locations must only contain axis names that are present in the Stylespace and from them only those that are not present in the font the Stylespace is applied to.
* Named locations must only use axes that are present in the Stylespace.
* All Stylespace name records must be provided in the same set of languages. If you provide a French name for one thing, you must provide it for all.
* Marked the library as containg typing information, so mypy can pick those up.