Handle headline_move error, when _get_re_string gets level=None.
To be consistent, though, do not jump to EOF/BOF on no header found. Was that usefulel? If yes, reimplement later.
Initial ST3 support:
* Fixed import statements;
* view.find now returns `(-1, -1)` instead of `Null` on nothing found, adjusted (prevents infinite loops mostly);
Merge pull request #17 from UNOwen/python3

ST3 support