[Issue #180] Updating documentation for lineHeightMultiple
Switching singleton implementation to use dispatch_once
[Issue 176] Removing non-object values from string attributes in order to prevent exceptions in NSCoding

Signed-off-by: Mattt Thompson <m@mattt.me>
Documenting NSCoding behavior for iOS < 6
Bumping version to 1.6.1
[Issue #186] Enmerate links in reverse so recently-added links have preference