Added zipdir library from a stackoverflow answer.

* Attribution correctly added.
zipsite now indlues site directory.

* Previously only .pth files were added and the site directory itself
  was ignored.
Added packaging.

* Currently capable of producing a zip file of a virtual environment
  that has a particular library installed.
Moved zipsite into data directory.

* This is because superzippy itself will never use the module, rather
  the bootstrapper will end up using it.