Improving the User Guide
More on the API docs.

Also, dropped the validator where the parser can do validation.
Fixed number parser which returned invalid for 0.
More work on the API docs

Creating the buttons after rendering the overlay, since I can't set
the event listeners until the section exists.
Added the current value as an argument to the buttons action arguments.
Dropped the number validator since the parser already validates.
Fixed the number parser which returned invalid for 0.
API docs improvement
Fixed the tests to match the recent changes.