Refactor Aspect Fill/Fit functions.
Tests! Are! Good!
Fix non-passing test.
Add an init methods that take a `method` parameter.

This gives calling code a way to specify the type of scaling to do: Aspect Fit (the default) or Aspect Fill.
Fix failing tests.

This raises an interesting problem: Should our processing libraries be checking `[UIScreen mainScreen].scale` themselves or should scale always be passed in? After this little gotcha with the unit test, I'm thinking the latter.
Refactor image retrieval.

We needed a way to get progress, so `sendAsynchronousRequest:queue:completionHandler:` had to go. We now encapsulate the load in `OGImageRequest` and use the usual delegate kung-fu (`NSURLConnectionDataDelegate` and friends)
[FIX #41860893]
Add support for rounded corner masking.
Add rounded rect masking via `cornerRadius` parameter.
Add cornerRadius to demo.