Single Contract process

[Harley Swick]

One suggestion I've received is to have a single process that handles all the requests for every contract. This seems to be a more idiomatic style for Elixir apps, where this process is in charge of any Contract related service. One benefit would be that this single process would be easier to pass around different modules, and you would only have to start it in the Application supervisor.

I was going to implement this and realized it is a very involved change because it completely changes the way state is handled starting from init to every single call. This would also be a very breaking change, so I think it is best to sit on it, and see what others think.