converted repo into proper package (name: tad; installable via setup.py)

Dear David,

I added some boilerplate to your code, which would make it installable
via ``python setup.py install`` (under the assumption that ``setuptools``
is already installed on the system).

The code is then importable via ``from tad import TADClassifier`` and the demo
can be launched from the command line with ``tad_demo``.

Cheers,
Arne