Embed nrepl server as complement to swank-clojure

Hi Håkan,

Very exciting to see the progress on deuce!

I'm not sure if this is of any interest, but since I'm using nrepl, I added support for embedding a nrepl server so I can poke around just like with swank-clojure.

Tested using:
```
lein run -q --nrepl
```

On a completely unrelated note, I had to bump the perm gen size with `-XX:MaxPermSize=128M` to be able to run/uberjar deuce, but I guess that's probably something you are aware of, related to the general performance. Also I'm running on `1.7.0_11-b21` on a OSX, and from what I gather you're on `1.8.0`.

Exciting stuff!