Fixes issue with tokenizer removing first selector after an unknown @ rule.

See discussion in #325.
Fixes #329 - font shorthands incorrectly processed.
Fixes invalid CSS in unit tests.
Refixes #325 - invalid charset declarations.

* All incorrect, non-lowercase charsets are being now removed.
* Removes stripping @IMPORT declarations.
Fixes #332 - background shorthand with none and color at the end (per spec).
Version 2.2.12.