Adding support for constant constraints (e.g. height = 150)
merging pull request #1
Updating the Readme with the new formula.

Also updated the podspec with the new version number. Will tag after this.
let -[UIView constrain:to:] return NSLayoutConstraint for debugging purposes
recognize subtraction operator. now you can do this:

    [button constrain:@"right = right - 10" to:view];
    [button constrain:@"bottom = bottom - 10" to:view];
Merge branch 'negativeconstants'