Add line to turn on the running of tests in parallel. Makes things fail. Will fix.
Started working on Viewport concept for scrolling interfaces.
Add Content class to track a virtual cursor within the content of the interface.
Add #refresh method to update the interface after the cursor moves.
Use correct range operator to remove requirement to alter value of #viewport_height.
Return height with #attrs, also;

- Add temporary #width method.
- Add more documentation.
- Simplify movement.
Add options.
Add Area class.
Add options for Compositor to #by_name.
Add Viewport class.
Require Area and Viewport.
Add unused defaults.
Experimental stuff for scrolling, cursors and geometry.
Remove options argument as no longer required.
Remove unused code.
Add more documentation.
Simplify by removing empty check and using #key?

- Whitespace.
Whitespace and add more documentation.
Remove commented out code.
Move exceptions into correct file.