All tag tests passing. Still need to finish backslash support and
support for templates and tags within <open> tags.

Conflicts:
	tests/test_builder.py

- Make a test in Py3k actually use StringMixIn instead of str.
- Minor cosmetic fix.

Conflicts:
	mwparserfromhell/parser/contexts.py
	mwparserfromhell/parser/tokenizer.py

Remove some extraneous whitespace in string_mixin.py.

Also add one for arguments.

Also add a couple for templates and one for integration.

Mostly by @gdooms, with tweaks.