Merge pull request #21 from hoelzro/master

More tests, fixes, and performance enhancements
Add an example overlay
Adding some failing tests
Toy UI Skelington
in progress with overlays
really basic overlay tool
Toy UI now has tabs!
generic algorithm for sizing and overlays:

The toy ui is helping make this easier to test.
Attempt to explain these magic numbers
refactor overlay function out of process_image
passing tests
Make a failing test, and escape overlay params that contain URL characters
Use requests to get the image data for an absolute url
Just use the existing image to get the height and width
removing unused variable
Include six for python3 compat and upgrade greenlet
use six for urllib dependency
Add a test for missing bg color attribute
Merge pull request #22 from steder/overlays

In progress: Use overlay templates to generate complex images (like product shots) from art
Fix typo