Test setup using combustion
Add a couple of specs to start off
Cut some noise
Various improvements + added tests
Validate presence of file
Introduce unique file tokens to be used as filenames

We do this to prevent issues arising with colliding file names if the application using the gem has
a setup that puts files in the same place (default) or has some other weird setup that doesn't
guarantee that files aren't overwritten.
Update readme with info regarding UUID-based filenames
Properly clean slugs
Add specs for JSON API
Fix combustion setup
Add capybara specs