Rewrite 
 to <strike> in cleanTree fn.
Use <S> to markup strike through, not <STRIKE>.

The <strike> tab has been obsoleted in HTML5.
Add support mult-level lists.

* Hit tab to increase list depth, or call increaseListLevel method.
* Hit enter on a blank item to decrease list depth, or call decreaseListLevel method.
Add kb shortcuts for making lists and +/- quote level.