Treat nil as not-an-attribute
Add methods for less-than/greater-than constraints
Improve naming of relation methods
Fix GitHub link
Sanitize version numbers in UltraLayoutTests
Fix forward class declaration build error
Rename and add new methods for creating but not adding constraints
Create an either-or AppKit/UIKit header
Move UltraLayout attribute methods into AttributeSet object

Reduces chances of future conflicts.
ULLayoutAttributeSet -> ULLayoutItem

A bit more semantic.
Move UIView+ULLayoutExtensions into ULLayoutItem
Make ULLayoutAttribute do something sane when passed a ULLayoutItem
Remove dead header
Update README to reflect move of UIView+ULExtensions
Add methods to constrain for various kinds of "next to"

The linkages aren't always terribly obvious.
Add methods to constrain an attribute to the superview's matching attribute
Add "Edges" to -[ULLayoutItem constrainTo{,Horizontal,Vertical}:]

Makes it a little clearer.