QUnit Interface: Adds support for built-in assertions, including expect()

This patch modifies the QUnit mocha interface to support all of QUnit's built-in assertion methods, including expect (the method that allows you to declare how many assertions are in a given test case).

I realize this is somewhat against the design philosophy of Mocha in that it ties assertion handling into the test runner, but in doing so it gains the ability to use the expect() method of QUnit, which requires some minor integration with the test runner to be able to work.

I've added tests, but since some of them are negative tests that are expected to fail, I haven't tied them into the build system though the makefile, as don't know if there's an existing paradigm for those conditions.

Feedback welcome of course!