Fontmake

- Added new ``--no-optimize-gvar`` to disable performing IUP-delta optimization when building TrueType variable fonts.
- When building variable font, apply the ``postscriptNames`` glyph renaming _after_ the variable font has been built, instead of on the master TTFs. This allows to use human-readable glyph names in DesignSpace ``<rules>``
(fonttools/fonttools1349, 551, googlefonts/ufo2ft332).
- Fixed issue with MutatorMath incorrectly "bending" masters' and instances' locations when DesignSpace axes contain `<map>` elements. If you used fontmake `-i` option to interpolate static instances from either Glyphs or DesignSpace inputs (and your DesignSpace axes contained any `<map>` elements), it is recommended that you upgrade fontmake and regenerate the instances (552, LettError/MutatorMath168).
- GlyphsLib v4.0.0 changed the way the width axis is exported to DesignSpace: if no `Axis Location` custom parameters are present, the user-space locations of the masters and the axis minimum/default/maximum are inferred from OS/2 widthClass of the instances. This makes sure that the static instances and the variable font's instances produced from the same source file have the width class. The change modifies the generated variable font's `fvar` and `avar` tables. If you generated variable fonts with `wdth` axis from Glyphs input, make sure you check this out. You can read more in the [glyphsLib v4.0.0 release notes](https://github.com/googlefonts/glyphsLib/releases/tag/v4.0.0), and at https://github.com/googlefonts/glyphsLib/issues/483.
- Bumped minimum requirements:

* fonttools >= 3.42.0

- Bump minimum required glyphsLib to v3.3.1. Version v3.3.0 contained a breaking change that needed to be reverted, because it modified the way fvar and avar tables are built for the `wdth` axis (googlefonts/glyphsLib483).

- Fixed issue generating interpolated instance UFOs (via MutatorMath) from Glyphs or DesignSpace input, when using the options `-i -o ufo`. The regression was introduced in v1.9.0 (3460616).
- Bumped minium required fonttools (3.41.0) and ufo2ft (2.8.0). See the respective changelogs for more details:

- Hotfix to fix 515.
- Bump fontTools minimum version to 3.37.3 to get https://github.com/fonttools/fonttools/pull/1477.

- Support sparse sources, i.e. source elements in Designspaces with a layerName attribute. Together with glyphsLib 3.2.0, this means automatic support for brace (and bracket) layers. Only outline and spacing information will be taken from sparse sources. Note that there's a bug in fontTools' MVAR generation code that is fixed upstream, but needs to be released (https://github.com/fonttools/fonttools/pull/1477).
- Added a CLI option `--expand-features-to-instances`, useful when making static instances while using a shared feature file in the masters. The option will expand the feature file to all instances, to avoid inclusion problems with the `include()` statement.
- Support making variable CFF2 fonts in the future. This currently depends on https://github.com/fonttools/fonttools/pull/1475.
- Bump minimum dependency versions to support the above.