Remove some extraneous whitespace in string_mixin.py.

Mostly by @gdooms, with tweaks.

- Also add tests for spacing in param names.

- Stop parsing new templates if the template depth gets above
  MAX_DEPTH (40) or if we've already tried to parse over MAX_CYCLES
  (100,000) templates.
- Add two tests to ensure recursion works somewhat correctly.
- Fix parsing the string "{{" with the Python tokenizer; add a test.

- Add a _SliceNormalizerMixIn to properly handle slices.
- Use floor division when applying key.step.
- Implement sort() without 'cmp' parameter.
- Fix bytes(list) behavior.
- Children of _ListProxies are now _ListProxies, not regular lists.

- Skip CTokenizer tests if CTokenizer is not available.
- TestStringMixin: Don't make assumptions about default encoding.
- Add urllib stuff to mwparserfromhell.compat.
- Fix compat.py's line endings.
- gen.next() -> next(gen)
- assert*Equals() -> assert*Equal()

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.