PyPI ready!

This makes pydown ready for the PyPI.

It adds a setup.py file that includes a `pydown` entry-point. So, after you install...

    $ python setup.py install

You can run `pydown` as a console script.

    $ pydown mypresentation.md mypresentation/


This also adds the `MANIFEST.in` (specifies which files to include) and `NOTICE` (licenses for vendorized packages) files.

The only thing you'll need to do to put this on the PyPI is

1. Register an account with the PyPI, if you haven't already
2. Run `$ python setup.py publish`.