Compositor now takes an interface for output;

Interface now has Geometry class to handle position and dimensions.
Revert change to Compositor.
Use print since we’ll be printing control codes etc.
Remove test_app; see http://www.github.com/gavinlaking/gitty for test implementation.
Add z axis- for layering interfaces on top of each other.

This won’t be implemented for a while I’m guessing.
Use class method instead.
Add Renderer to output the composition stream;

- Update README.
Compositor’s role is to produce the stream;

- Add helper methods to Compositor and Geometry to facilitate this.
- Update README.