Ufolib

- Minor fixes to validation
- Make validation on the default for read and write (prior it was off for write)

- Fixes issue whereby the required lxml dependency was not correctly specified in the setup.py's `install_requires`.

- Added options to turn validation off on read and write. This can be globally, or per bit of data. For UFOWriter, validation is on by default. For UFOReader, validation is off by default.
- Switched to lxml from ElementTree. lxml is now a required dependency.
- Optimizations to glyphLib (adrientetar)
- When converting to UFO3, ufoLib will now remove the older mmk group prefixes

- Clarify license, copyright and trademark strings for test fonts. They
now explicitly point to the license of the package (100).
- Ignore renameGlyphSet and deleteGlyphSet when formatVersion < 3 (91).
- Make fontLibValidator errors more verbose.

None

First public release with UFO3 support.