Fix failing tests.
Move some system events into respective modules.
Add #show_cursor and #hide_cursor commands to Cursor.
Add methods from Position to Cursor;

- Add default values for top and left.
- Position is starting to become redundant.
Update Cursor;

Use the interface's geometry for basis of position.
Prefer $LOAD_PATH to $:.
Handle Fixnum as a defined value.
Don't need this anymore.
Add more documentation.
Remove `cursor` from interface API, also;

- Add Cursors class to track position and visibility of all interface cursors.
- Move Cursor into models/.
- No longer render the cursor as part of an interface refresh.
- Refresh cursor when interface focus changes.
- Refresh cursor for focussed interface when terminal resizes.
Add basic 'cursor_app' to demonstrate cursor usage.
Add name to Menu instance, also;

Defer building of collection into a Menu object until we store the menu.
Add more documentation.