Reset Keymaps before each test and tidy up.
Add more documentation.
Refactoring;

- Move query methods into single method to DRY up.
- Update tests.

Note: I don't like how the Compositor is asking the buffer if there is content on each of the buffer types, and then rendering/clearing based on this. I think this logic belongs in the Buffer class.
Add placeholder tests for API.
Add placeholder DSL integration tests.