Version 1.0.0

This is a full rewrite of SwiftAutoLayout with the following major changes/additions:

• Setting layout priorities is supported using the ~ operator
• Support for UILayoutGuide and NSLayoutGuide
• Support for constraining using UIViewController layout guides
• Layout item types are now parametrized using a shadow type that determines whether the constraint is an X axis, Y axis, or dimension constraint for additional type safety
• The al_ prefixes have been dropped from the layout item accessors (e.g. view.al_left is now view.left)
• The method equivalents (e.g. greaterThanOrEqualTo() instead of >=) to the operator overloads have been removed since these are needlessly verbose and do not add much value over using the (NS|UI)LayoutAnchor API