add @2x only
fix some bug
Merge branch 'master' of git://github.com/zhfish/KSImageNamed-Xcode into pull-request-24

Conflicts:
	KSImageNamed/KSImageNamed.m
	KSImageNamed/KSImageNamedIndexCompletionItem.h
Making code style match from PR #24.
All file-based images are now referenced as "1x and 2x", "1x only", or "2x only" to ensure everything is extra clear.