Local font subsetting

Breaking changes:

• Removed --format option. Subfont now automatically generates woff2 and woff files
• Switched font-display default value from auto to swap
• Renamed --inline-subsets option to --inline-fonts

Features:

• Added --[no-]recursive option (@papandreou)
• Added ability to subset locally with fonttools. Allows working with non-google fonts #3 #1
• Warn when glyphs are missing in original font #13
• Preload fonts with Javascript for browsers without preload support #5
• Output both woff2 and woff formats #4

Patches:

• Don't break when encountering existing preload hints for fonts