Continuous playback when scrolling in UIScrollView

Let's stress test this!

See: https://github.com/Flipboard/FLAnimatedImage/issues/6
displayLayer needs to return the still image in case no animatedImage exists so the image is visible.
Disable highlighting for animated image view

UIImageView highlighting breaks FLAnimatedImageView for animated images.
Ensure smooth scrolling on older hardware
Merge pull request #31 from Flipboard/scrolling-playback

Continuous playback when scrolling in UIScrollView
Code gardening: remove superfluous whitespace
Implement intrinsicContentSize in image view

UIImageView returns its image size as its intrinsicContentSize so that Auto Layout Just Works.
Import UIKit in FLAnimatedImage.h

Since UIImage is referred to, we need to import UIKit. Otherwise we can get build errors about "Unknown type name 'UIImage'".

Moreover, importing UIKit obviates the need to import CoreGraphics in FLAnimatedImage.m.

Fixes #36
Merge pull request #34 from NikolaiSa/InvisibleStillImageFix

displayLayer needs to return the still image in case no animatedImage ex...
Add fine-grained logging with an auto-detect CocoaLumberjack integration.
Update README
Merge pull request #42 from Flipboard/cocoalumberjack-logging-integration

CocoaLumberjack Logging integration
Merge pull request #38 from nolanw/intrinsic-content-size

Implement -[FLAnimatedImageView intrinsicContentSize]
Code gardening: add whitespace for style consistency
Restructure code to simplify program flow.

This way we don't have an uninitialized local variable "for a little while". We always would assign a value to it in the if-else block below, but it seems like a good practice to avoid uninitialized variables in general, in case the code around it changes.
Merge branch 'nolanw-disable-highlighting'

Conflicts (Resolved):
	FLAnimatedImageDemo/FLAnimatedImage/FLAnimatedImageView.m
Better grouping of code and add comment to clarify.
Merge pull request #37 from nolanw/fix-imports

Import UIKit in FLAnimatedImage.h
Fix potential crash during memory warning.

This could happen when the object entered dealloc on a background thread and at the same time received a memory warning notification to handle (on the main thread).

The solution suggested by @ryanolsonk is bailing in the handler when the weak reference to self is nil'ed out by the weak system.

This change also removes a previous attempt at fixing this observed behavior by holding a strong reference to self, where we wrongly assumed that NSNotificationCenter no longer grabs a strong reference to the observer before notifying.
Improve macro to detect CocoaLumberjack during compile-time.