Add support for "not" operator

[disnet]

Want to write a contract like:

f :: (not Num) -> Bool
f = ...

Little tricky since "not" lexes down to "!" which we claim for escaping the contract expression.

[gregwebs]

I personally have not felt the need for this yet. white-list is a much more exact approach than black list.

[disnet]

Good, I haven't been needing too badly either. It's just a convenience anyway since you can always do NotNum = ?!(x) -> typeof isnt 'number'

Would still be nice to fill out at some point though.