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
Line is too long. [94/80]<br>Surrounding space missing for operator '=>'.<br>Space inside { missing.<br>Space inside } missing.