Now there are namedtuples for PDO types, and two functions to help with
reading PDOs from the Sink.  They're all tested, and our test coverage
is now at 98%(!).

Rather than having one method doing double-duty as getter and setter,
with ugly syntax, why not use a property?  Now the Sink's output can
simply be read and written as a boolean.

The README has been updated to show how to manipulate the new SinkConfig
objects, as well as what the output really looks like now.

Whoops!  The version that was pushed to PyPI is correct, but I forgot to
commit the change.

The library has now been tested with Python 2.7, 3.3, 3.4, 3.5, and 3.6.
The README and setup.py now indicate this.  The README also says how to
run the tests, and that you need a PD Buddy Sink plugged in for them to
be completely thorough.

One extra dependency is pulled in for Python versions older than 3.6,
but other than that it's pretty easy to support them.  It definitely
works on 2.7 now, and should work on older 3.x versions (but that's
untested).

It's the preferred format for Python, after all.

We use some 3.6-specific features from the enum library, so older
versions won't work.