Implemented __nonzero__ for Interval types.
Use nose.tools.eq_ instead of bare asserts.

The eq_ function offered by nose allows you to pass
an informative message to the assertion, which will be output on
test failure. Should be much more useful for complex cases.
Typo fix.
Refactored tests to use nosetest convenience functions.

Tests will use ok_ and eq_ to leverage the msg arguments,
making diagnosing tests quickly much easier.
Implement __add__ for Intervals.

__add__ will return a new Interval object with the start and
left closedness of self, and the end and right closedness of
other. With passing tests.
Refactor test_equal_intervals.

No need to build a whole separate object to test equality. Simplifies
test cases, mostly.
Change tox.ini to use py.test.

I'm switching to py.test for better failed-test outputs. The
pep8 plugin will also be pretty useful.
Change Interval.__str__  to Interval.__repr__.

I realized that str() falls back to repr(), and that most
test runners rely on the repr() of objects. Who cares about
these things' memory addresses?
Adding __add__ method and some passing and some failing tests.
PEP8 Compliance.

Now that the test suite has PEP8 compliance checking, I took some
time to update this code to be compliant. Starting now merges into master
will have to pass the PEP8 check.
Merge branch 'pep8' into interval_comparisons

Merging this into here pending passing tests, for a merge into master.
Still need nose for the tests. For now.
Changed unit test's message output for clarity.

Also meeting PEP8 compliance.
Updating unit tests for correct testing.

Some of the subclasses of OpenInterval didn't implement their own
instance of test methods that were logically flawed (for the subclass).
Correcting more incorrect assumptions in the tests.
Merge branch 'interval_comparisons'

This is a big merge. Interval type now supports +, &, <, and <=. Also
brings a full passing test suite and full PEP8 compliance, both of which
are henceforth required for merges into master.