Fix CPLayoutConstraintTest demo constraints. We are more strict (like cocoa) about the required number of constraints for a view.
WIP
CPContentSizeLayoutConstraint support for constant mutation. Initial invalidateIntrinsicContentSize support.
Test for invalidateIntrinsicContentSize
Progress with compression/hugging. Updated test invalidateIntrinsicContentSizeTest.
CPLayoutConstraint: Added CPLayoutVariable(view, mask) utility function. Code cleanup.