FIX: Fixes

@rougier this was (just about) the minimum required to get `gl-agg` running on my OSX laptop. I tried installing it on Ubuntu earlier today (before making these changes) and that didn't work either, I can see if these changes fix that, too.

Closes #1.
These were the not 100% necessary changes, but they make it clearer that the imports should be relative (not absolute).