Add support for Cowboy.

Also updates README with info regarding Cowboy.
Merge pull request #10 from rabbitmq/master

Avoid use of non-dfsg-free json.js
Merge branch 'add-cowboy-support'
Update overview text.
blank rebar.config file
Merge pull request #11 from zkessin/master

Added a rebar.config file
Update cowboy API calls to make it work in 0.8.0
Merge pull request #13 from sedinin/master

Cowboy 0.8.0 issue