API Doc: images controller
change favourite attribute description
add images_controller doc example
specs for images-controller and add examples to apipie doc
apipie doc and rspec-examples for items-controller
Rename controller action generate_cloudinary_signature to generate_signature to match route (and therefore documentation).
Add more detail re: donation_condition_id
Add more detail re: rejection_reason_id. Use state_event instead of state as this will fire the transition helpers.
Fix a couple of allow_nil options in documentation.
Ensure exceptions in test mode are more verbose.
Using DonorConditions and RejectionReasons in documentation wreaks havoc with specs... reverting Steve's changes! :)
Refactored test
Rebase with master

Conflicts:
	app/controllers/api/v1/offers_controller.rb
Merge pull request #16 from crossroads/api_doc_images

Api doc images and items controller