Align 2.0

Use Migraiton Guide included in the repo to ease migration.

• Add macOS support
• Add new low-level APIs: equal, greaterThanOrEqual, lessThatOrEqual
• Add spacing() method for alignments
• Rename uncler .al to .anchors
• Remove .al version accepting closure
• Add constraints property to Constraints type to allow access to all of the constraints created using it
• Add activate parameter to Constraints initiliazer to optionally disable automatic activation of constraints
• Deprecated func edges(_ edges: LayoutEdge...), use pin(axis:) insteads
• pin() methods now use .leading and .trailing anchors intead of absolute .left and .right anchors. To switch to absolute anchors, use absolute(): view.anchors.edges.absolute()
• Remove addSubview family of APIs
• Migrate to Swift 5.1
• Increase minimum required platform versions