Uses six.u() to allow Python 3.2 compat.
Merge pull request #285 from thomasgoirand/master

Uses six.u() to allow Python 3.2 compat.
At last, real parsing for url().  Partly.  #192
Revert "Uses six.u() to allow Python 3.2 compat."

This reverts commit 65235576e1076a93c6c9ed06ba657105bea6b012.
Remove u prefix from files that use unicode_literals.
Fix parsing of at-rules; newlines were not treated as whitespace.  Fixes #260.
Improved escaping/unescaping and dequoting of strings
Fonts glyph codes are now just plain hex numbers
Compiling of source_files is done later (was it being done twice?)
Accept '-' as the stdin file name
Header argument might not exist
Grammar was using wrong (undefined) variable.
Urls could contain variables and other things (at least consider urls which might contain variables)
Compare expected (unicode) with actual (also unicode)
Merge remote-tracking branch 'Kronuz/master' into compat_win