add beforeEach and afterEach

[bpytlik]

This adds support for the beforeEach and afterEach test setup functions. They mirror the ones that exist in mocha. beforeEach functions are run before any test specific before functions. afterEach functions are run after any test specific after functions. I think this also provides a fix for issue #20. It doesn't expose it in beforeAll, but it provides the necessary functionality (I think).