The below things should be fairly straightforward to implement. Just look in
the commit logs at how similar features were implemented.

* 'loop' keyword. (at least the infinitely looping version is easy.)
* 'repeat' keyword.
* 'LEAVE', 'FIRST', 'NEXT', and 'LAST' phasers.
* 'goto' keyword.

All contributions are welcome; especially those with good test coverage and a
consistent writing style.
