Strong reference to targetItem in LayoutItem can cause memory leak

[t089]

The LayoutItem tuple contains a strong reference to the targetItem view. This can cause a memory retain cycle if the view itself maintains a strong reference to the layout item tuple.

Manuscript/Sources/LayoutItem.swift

Line 34 in bb21c1c

public typealias LayoutItem = (constraint: NSLayoutConstraint, targetItem: UIView)

Maybe a possible fix would be to make LayoutItem a final class with a weak reference to targetItem.

Of course the necessity of LayoutItem is questionable in the first place, because the layout constraint already has a unowned (!) reference to the two parties participating in the constraint (firstItem, secondItem).