Added macros checking for Retina display, iOS7, and to add -568h postfix to NSString if running on iPhone with 4" display.
Added - (CGSize)backCameraStillImageResolutionInPixels;
Added - (BOOL)isIphoneWith4inchDisplay;
Obtain size of buffer from sysctl instead of constant.
Merge pull request #7 from IvanRublev/master

Several useful hardware check macros and methods are added. Buffer size fix.