Externalized configuration settings, updated documentation and added Dockerfile

[osterman]

Please check out these changes. Hope you don't mind that I took some liberties and moved sample configurations to the contrib/ folder.

Other than that, I moved the limits and log level into the external config so that the core doesn't need to be modified. On my CoreOS cluster, load is usually higher than 0.9 =) The configuration file path is now configurable with an ENV.

Also, updated the sample configuration with support for ENV variables. This works for a simple, single server-upstream use-case. e.g) I run one unrealircd, but need to proxy requests from multiple CoreOS servers that expose a public port which should tunnel back to the ircd.

I've also added a copy of my Dockerfile which I'm using to build an image that I deploy on CoreOS.

Thanks for sharing this irb lb. There's nothing else out there!

Totally understand if you don't accept this pull request because I made some opinionated changes.

Cheers!

-Erik