Glyphslib

- Fixed issue when building UFO from .glyphs file containing layers that are associated with a non-existing master, or layers that don't have a name.
These are now skipped, and a warning message is logged (282, 291).

- Fixed issue parsing 12h formatted datetime (274).
- Fixed error parsing source file saved with Glyphs.app >= 1082 (https://github.com/googlei18n/fontmake/issues/374, #267, 286).
- Allow to generate `glyphdata_generated.py` from supplied xml files (287).
- Read colors and set UFO keys for Glyphs ColorIndex and public.markColor (285).
- Added support for "Replace Feature" custom parameter (289).

- The new `glyphsLib.classes` module provides an API that should match the internal Python API of Glyphs.app: https://docu.glyphsapp.com/
Note that currently not all the classes and methods may be fully implemented. We try to keep this up to date with upstream, but if you find something that is missing or does not work as expected, please open a issue.
- The library now supports round-tripping (read/write) .glyphs files that were produced with Glyphs.app >= 2.5b (1076) without additional changes. If some Glyphs data doesn't round-trip, then it's a bug. Also, if you edit the Python objects (instances of GS* classes) before writing to .glyphs, then diff between the original Glyphs.app file and the modified one should only reflect the changes that were made to the Python objects.