Minor Cleanup

Just came across your library and noticed a small things I thought I'd try to lend a hand to help with, hope it is helpful.

1) Per Apple's [Coding Guidelines For Cocoa] (https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/CodingGuidelines/Articles/NamingMethods.html#//apple_ref/doc/uid/20001282-BCIGIJJF) section on naming guidelines, delegate methods should include as their first argument the delegating object and identify the object by its class. For example `-tableView:heightForRowAtIndexPath:`
2) There are a couple spots in `NBNPhotoMiner ` where a block argument was mandatory (it is called without checking whether it was `nil`). I added some NSParameterAssert calls which will help make those requirement easier to determine/debug while developing rather than waiting for a crash to happen which may or may not produce a useful stacktrace.