Beta Gluten

Support for the GF Latin Plus requirements ( https://github.com/googlefonts/gftools/blob/master/Lib/gftools/encodings/GF%20Glyph%20Sets ).

Lots of curves here, so there will probably be many little adjustments before v1.0, but it is very close (and stable).

Alpha (v0.9) Gluten

Stable but still some work to do (curves, language support).