Skip test_readme_5() if web query fails.
Apply bugfixes so that some tests pass on Python 3.

- 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()