Implement PDF processing. Includes:

* Numerous spec improvements
* Refactor the existing processor classes to have more logical names
* Create a way to dispatch to different processors based on mime types
* Fix the carrierwave config
* Remove unused minitests

Todo:

- [ ] Implement the logic that actually parses PDF content
Use the new Ruby 1.9 hash syntax.<br>Prefer single-quoted strings when you don't need string interpolation or special symbols.