Use gorilla mux as router

[marcotroisi]

It appears that with the default router we're currently using, we're not able to set up regex-based endpoints, allowing us to do things like GET /users/{id}.

We need to integrate the gorilla-toolkit mux and use it for our go-kit endpoints.

[marcotroisi]

The first thing to do is something like this. A general HTTP handler based on gorilla mux's routes.

[marcotroisi]

Currently getting {"error":"EOF"} when running a simple curl -X GET localhost:8080/user/2`. Possibly something is not right with the response, and perhaps we're not printing anything. Need to investigate.

[marcotroisi]

PR: #35