Make installable package.

This pull request makes a package from what was a script before. Rather than word_freqs.py, I went with the package name `redditwc`. One installed the executable to be used is just `word_freqs`.

The package name is pretty important so I wanted to get your feedback on that before merging this. There are really two things necessary to decide:

- [x] What is the package name? (currently `redditwc`)
- [x] What is the executable name? (currently `word_freqs`)

Once we have this, installation will be as simple as `python setup.py install` for anyone who checks out the source, and once we add it to pypi, then all that will be needed is `easy_install <PACKAGE_NAME>`.