Making Rakismet Thread-safe

While investigating Rakismet to see how it obtained the request-related information, I noticed that a lot of the information was being stored in non-thread-safe class instance variables. Considering the larger number of people deploying onto Puma and other thread-capable servers nowadays, this seems like a large omission.

So here's a change set to store the request and responses in Thread-local variables to keep thread safety.

The tests also still pass, a large majority of them are now rewritten to use expect/allow from rspec 3.