Removing RecurrenceModelField, which doesn't work

Our current best guess is that this code used to work in
older versions of Django, but it isn't used by any of the
core maintainers, and no one's complained that it's broken,
so I feel relatively safe removing it.

This change is noted in the 1.1.0 release notes.
Adding documentation headers, and more API usage
Make local documentation builds use the RTD theme
Removing extraneous whitespace
Updating docs to record that we run tests on Python 3.4 now too
Removing now unused imports
Add tests for the way "between" works if no limits are set up