remove redundant `CGImageSoureCopyPropertiesAtIndex`
adds scaling method to key.

This fixes a subtle bug where if you scaled an image using one scale method, then requested the same image at the same size but with a different scale method, you'd get a hit from the cache for the earlier image (i.e., the wrong scale method)
adds `OGImageView`

`OGImageView` is a subclass of `UIImageView` that encapsulates all the behavior of `OGImage` (specifically, `OGScaledImage`) to handle the most common case of loading an image from a URL
and displaying it.
updates demo for `OGImageView` and iOS 7.
Updates readme with description of `OGImageView`
readme link formatting
adds mo' readme fixes.
Minor formatting in README.md
Merge branch 'master' into develop
Merge branch 'develop' into ogimageview

Conflicts:
	OGImageDemo/OGImageDemo/OGImageTableViewCell.m
	OGImageDemo/OGImageDemo/OGViewController.m