Use faraday to make backends interchangeable and 
expose the faraday config
Updated Readme

Added missing block arg in config example.
Update README.md

fixed typos
relaxed patron runtime dependency so that it can still run on old version of patron as we need the new one only for dev.
Merge pull request #23 from thilo/faraday

Use Faraday as HTTP connection library, brings interchangeable adapters and middleware