Add a note about tox
Add experimental support for Python 3

Code coverage still isn't great (62%), so I don't promise it
all works, but all the current tests pass.
Add simple tests for form field cleaning
Improve the error message format for bad parameters
Fix typo in variable name

Previously, specifying an invalid frequency would cause
KeyErrors on validation, since we wouldn't be able to find
the error message correctly.
Dead code removal - nothing in deserialize raises ValidationError

The only place that raises ValidationError is in
serialization code, not deserialization code. Serializing
ends up calling validate, but deserializing does not.
astimezone is a method on datetime.datetime, not datetime.datetime.tzinfo

Also, factoring out a common chunk of code to reduce
duplication.
rule_model.until is not required, so cannot be presumed to be set
Neither Rrule nor Exrule exist - I presume Rule was intended here
Test for the rule manager
Fix copy-paste error in loop over exclusion rules
Fix for handling dates that may or may not be timezone-aware

I'm not entirely certain any of this code is a good idea,
but at least we're now consistent about how we handle
timestamps.
Tests for the recurrence object manager
Ignore the docs build directory
Development version number bump to 1.0.4dev