Add Faraday as a dependency and add .rvmrc to .gitignore
Add faraday_middleware and simple_oauth as dependencies
Use Faraday for requests
Replace oauth gem with Faraday completely

This is just a prototype. It's probably a good idea to write a separate
oauth gem replacement based on Faraday and use it in dropbox-api with
almost no changes.
Add :token and :secret accessor to RequestToken

Compatibility with oauth gem.
Merge pull request #2 from petems/faraday

Faraday stuff