Glyphslib

* Apply master custom params _after_ writing master UFO features
* Roundtrip bracket glyph kerning
* Better error message for when decomposing backgrounds hits non-existant glyph

Make sure that detaching bracket glyphs get their own production name.
This avoids spurious public.postscriptNames overwrites on roundtrips.

* Fix infinite loop in GSPath.segments (621)
* Fix applyTransform for paths (625)
* Fix out-of-order array access in bezierminmax (627)
* Improve vertical typesetting (629)
* Fix problem where axis with no mappings was erroring out during roundtrip (630)
* Use Proxy for GSFont.features/featurePrefixes (632)
* Improve compatibility with Glyphs: Make GSNode.position settable with a tuple. (644)
* ufo2glyphs: Make really sure to preserve the Designspace axis order (649)

CI is now done via GitHub Actions, thanks to Simon & Cosimo.

Testing automatic deployment via Github CI.

- Added support for "Axis Mappings" font custom parameter (618, 568).
- Accept floats in brace layer name definitions (616).

Fixed two issues with anchor propagation in composite glyphs (617, googlefonts/fontmake682).

1) marks that are in turn composed of other marks (e.g. "shadda_fatha-ar") didn’t receive propagated anchors at all. A solution was already developed in ufo2ft's `PropagateAnchorsFilter`, so Yanone ported that piece of code over here.
2) ligature anchors (top_1, top_2 etc) weren’t correctly propagated when composed of base glyphs and a mark (e.g. "lam_alefHamzaabove-ar"). To fix that, we now check for marks attached to a named `GSComponent.anchor` (stored in UFO as `Glyph.lib['com.schriftgestaltung.Glyphs.ComponentInfo']`), and adjust the named anchor’s position by the component transformation.