Add functionality to mochalite.js framework:

• it.skip(...)
• it.only(...)
• describe.skip(...)
• describe.only(...)

I anticipate that these will be local to the individual test file (as in, one committed "only" won't knock out every other test everywhere).

Some prior implementations to learn from here: https://github.com/10gen/mongo/compare/master...skunkworks-happyjstest