DFImageManager 0.3.0

• New, rock solid DFImageManager implementation based on finite state machines, 25% smaller. The FSM code is based on ImageManager implementation from Nuke (experimental DFImageManager analog written in Swift).
• Add DFImageManagerErrorDomain and DFImageManagerErrorCancelled. The DFImageManager now guarantees that completion block for the request is called when the request is cancelled.
• DFImageRequestID implements NSCopying protocol and can be used in dictionaries, sets, etc
• DFAFURLImageFetcher now tracks progress of data tasks
• Fix DFImageRequestOptions priority that can now be used on iOS 7 (@andrebraga)
• Fix crash when using DFImageProcessingCornerRadiusKey (@andrebraga)
• Fix an issue when UIImageView (DFImageManager) wasn't canceling requests.
• Remove -cancelRequestWithID and -setPriority:forRequestWithID: methods from DFImageManagingCore protocol. There is a single way to cancel request or change its priority (using DFImageRequestID)
• Remove -startPreheatingImageForResources:targetSize:contentMode:options: and -stopPreheatingImageForResources:targetSize:contentMode:options: methods from DFImageManaging protocol. There is now a single way to start/stop preheating using -start(stop)PreheatingImagesForRequests: methods.
• Streamlined DFImageManaging protocol. Remove DFImageManagingCore protocol.
• Remove allowsSynchronousMemoryCacheLookup option, this option is always on.