Use Unicode literals everywhere

Note that in Python 3, `re` does not interpret r'\x##', r'\u####'
and r'\U########' escapes. Replacements relying on these, such as
    ur'\u201E\1\u201C'
are converted to e.g.
    '\u201E\\1\u201C'
Establish Python 3 compatibility using a simple compat module
Update metadata to say we're Python3 compatible
Merge pull request #15 from encukou/py3k

Py3k