Added rakefile, converted to NUnit, created nuget package

This relates to #3 #5 #2 

I have converted to NUnit and added the rakefile. I still need to handle the native compiling next. All tests still pass.

To run you'll currently need ruby, and the bundler gem installed. After that from the directory run either "rake", or "rake ci" The former will compile and run the tests and the latter will do both and produce in the artfacts directory the nuget package.