Move test directory to top level

The test directory should be in the top level, separate from the rest of the
application. A future commit will create a separate pip.req file for test
dependencies only.
Update test README and structure

The testing directory is now separate from the main application and the
instructions for testing have been updated. It will obviously assume that shrunk
has been installed in a virtualenv but for now it won't be listed in pip.req.

Perhaps a future commit will add a setup.py; this will allow for easy testing
with:

    (virtualenv) $ python setup.py sdist
    (virtualenv) $ pip install --no-index=--find-links shrunk0.1/ shrunk

or something similar.
Update .gitignore to ignore compiled files

Now also ignores __pycache__ directories generated by iPython.