Allow Data URI Schemes

From https://en.wikipedia.org/wiki/Data_URI_scheme, allow the psuedo-protocol 'data'.
Allow the data URI scheme, a whitelist for content types, and update tests to correctly check URIs
Guarantee we use an allowed protocol
Add ourselves to AUTHORS file
Use six to import urlparse
Rename and move content type regex to the top of the file so we only compile it once
Don't check the encoding or the data, and switch charset and encoding to non-capturing subpatterns