Updated repository and sources to prepare for Google Fonts.
- Converted Overpass.glyphs back to Glyphs 2 as our build process can't process Glyphs 3 at this time.
- Cleaned up metadata in the source files. Renamed and adjusted things here and there.
- Added more metadata files (AUTHORS / CONTRIBUTERS) which should be reviewed.
- Added Makefile process with config files. Will also build on the github server.
