setup plugin

For this I needed to do a lot of stuff.

First, convert the dir structure to one that supports packages and scripts, but is also the one suggested in several places:

  * http://learnpythonthehardway.org/book/ex46.html
  * http://stackoverflow.com/questions/193161/what-is-the-best-project-structure-for-a-python-application
  * http://as.ynchrono.us/2007/12/filesystem-structure-of-python-project_21.html

Second, fix the imports internally.

Third, rename `source_paths` to `packages`, which personally makes more sense, and add `scripts`.

Finally, we have the plugin itself.

As final notes, we will probably need to make a cookiecutter template for this dir skeleton; and probably this plugin could call the one that generates the binary from the `entry_point`.