Adds two new operators.

* Adds the `!in` operator as a convenience over the more verbose `!( x in y )`.
* Borrows the null coalesce operator from C#. `??` will check if a value is null or undefined.
* Adds tests for the new operators.
Nuking null coalescing operator.
Merge pull request #8 from Syke94/master

Adds two new operators.