Added APParallaxViewDelegate protocol with optional methods APParallaxView:willChangeFrame: and APParallaxView:didChangeFrame:
Fixed delegate method names and updated demo project
Updated readme
Updated podspec
Merge remote-tracking branch 'upstream/master'

Conflicts:
	APParallaxHeader/UIScrollView+APParallaxHeader.h
	APParallaxHeader/UIScrollView+APParallaxHeader.m