Add from __future__ import unicode_literals to a few files.

Still need to do some py3k-only ones.

- Newlines are now allowed in template param names.
- Changes also affect handling of arguments like {{{foo}}}.
- Update unit tests: remove some unnecessary ones, and add some to cover the changes.
- Update StringMixIn tests to actually work for some of the methods.
- Update copyright notices for the C extensions.

Some other changes, including removal of the 'string' import in the tokenizer.

Also, fix parsing of wikilinks in both tokenizers such that newlines
in any location within the title are an automatic failure.

Still need to do attributes.