[catalog] Modernize CustomTextAttributedLabelViewController.m.
[attributedlabel] Deprecate attributedString. Use attributedText instead.
[attributedlabel] Modernize NIAttributedLabel.h.
[attributedlabel] Begin cleaning up the attributed label source.

- Document constants.
- Prefix local functions.
[attributedlabel] Add strict compiler checks for iOS 6 base SDK. Modernize more of NIAttributedLabel.m.
[attributedlabel] Delete pre-iOS 6 code.
[attributedlabel] Delete all /// dividers.
[attributedlabel] Delete all synthesizers.
[attributedlabel] Support iOS 7 with linkColor by using tintColor.
Merge branch 'attributedlabel'