Add SetUp and TearDown methods

I added SetUp and TearDown methods that can be overridden in user specs to run code before each logical test, like NUnit allows you to do. 

SetUp runs before the first Given() (or When() when no givens are used) and TearDown runs after each Then().

I also added a test project that shows the methods work. It also includes an implementation of FizzBuzz that matches the tests / output in the readme.