Fully-qualified all imports in __init__.py.

This is slightly uglier than the existing `from .blah import X` but I
suspect it will fix #28. I have no way to test this but it passes
`nosetests` on 2.6 (I'll let TravisCI tell us about 3.x).

Minor tweak - made setup.py executable since I am in the habit of
typing `./setup.py develop`.

@mrocklin - can you think of a better way to do this?  Issue #28 is a complete showstopper for me being able to use this library.