New gitignore
When deleting a component from a glyph, _endBaseGlyphObservations assumed the base glyph is present in the font. This does not have to be the case. A component can reference a glyph that doesn't exist.

Note: _beginBaseGlyphObservations also makes the same assumption. I'm not sure why I'm not tripping that error.
Merge pull request #11 from LettError/ufo3

This looks good. Thanks!
Allow DefconError to contain a report.
Use the new kerning validity error system.
Be smarter about locating the referenced glyph.
Fighting with git.
Support the new UFOWriter down convert kerning group mapping.
Merge pull request #1 from typesupply/ufo3

update from Tal's UFO3 branch