- Added UIButton+RUTextSize.

 - NSString+RUTextSize method -textSizeWithBoundingWidth:attributes: now is iOS 7 only, since it uses boundingRectWithSize:options:attributes:context: which is also iOS 7 only.
 - UILabel+RUTextSize now checks for textSizeWithBoundingWidth:attributes: responder.
 - UILabel+RUTextSize now can absorb from a UIButton.