Refactor the cancel logic
Merge branch 'master' into new_cancel_logic

Conflicts:
	SDWebImage/MKAnnotationView+WebCache.m
	SDWebImage/UIButton+WebCache.m
	SDWebImage/UIImageView+HighlightedWebCache.h
	SDWebImage/UIImageView+HighlightedWebCache.m
	SDWebImage/UIImageView+WebCache.m
Merge pull request #771 from Whirlwind/new_cancel_logic

Refactor the cancel logic
Added comments and coding style to previous pull request #771
Update for #771 - instead of removing the old methods, deprecated them so we are backwards compatible.
Fixed #775, made sure all the category methods that are public have the sd_ prefix (deprecated the old ones)
-there were a few exceptions where I just renamed the methods since they were added in this method
Added option to use the cached image instead of the placeholder for UIImageView. Replaces #541. Fixes #599
Fixed misspell
Updated README.md with badges
Merge branch 'master' of https://github.com/rs/SDWebImage