Added PATCH support

Added quick PATCH support. I didn't have the time to read the full codebase, but by following the call chain of PUT, this seemed sufficient.

Tests are also superficial as I just copied the PUT tests.
This version won't build yet as node-simple-router doesn't support PATCH, however I have filed a pull request in that repo as well. Aside; why use node-simple-router in the first place? With all respect, that project seems like a one off to me. Why not use express, which is well maintained?

I will build and send another pull request once the mock server works, so test can pass.