Introduce an error class for data URL errors
Test that we ignore gibberish in base64 strings
Allow URL escaping in base64'd data URLs

A close reading of the standard seems to indicate this is the proper way to interpret things.
Test that no-comma data URLs are rejected
Handle URL-encoded type fields
Default content-type to ASCII text

Matches RFC 2397.
Test parse fields separately

So we don't end up failing because an irrelevant field changed
Bump to version 0.0.2