Tests for the Runner class

Added more tests for the runner class and updated the code so it passes
them.
Added test for runner the correct handler.
Added Usage class

Added the Usage class to separate the concerns from the runner,
consolidating the printing of the help screens into a class which an app
using Glint can also use to provide custom help functionality.
Integrated the Usage class into the Command class.
More tests for the Runner class

Added tests around throwing exceptions when invalid calls are made.
Added setup functionality
Moved the test script into the examples folder.
Added a second example.