Something not working with setup.py package_dir
Rename `tests` directory to `test`.

Per
<http://docs.python.org/2/distutils/sourcedist.html#specifying-the-files-to-distribute>,
this ensures that test files are automatically pulled into source
distributions.
Fix multiple installation issues.

  - Make sure package is installed properly (thanks @loisaidasam).
  - Rename tests directory so it is included in sdists.