dev.twitter.com is now a big promo page for fabric.io (mobile development bs with a waiting list), and has no easy-to-find link to the apps page. It's more helpful to link to their app management page directly.
* Moving contributing guidelines to their own file.
* Changing the `key` and `secret` names to match the names used by
Twitter. This just reduces friction and helps those unfamiliar with
Twitter OAuth get started.