Moved `public func ==(_:_:) -> Bool` into type extensions as static functions to properly adopt the `Equatable` protocol.
All instances of `isEqual(to:)` have been replaced with `==`, but the `isEqual(to:)` methods remain for compatibility with objective-c

…quatable

According to [Apple](https://developer.apple.com/library/content/documentation/Swift/Conceptual/BuildingCocoaApps/InteractingWithObjective-CAPIs.html#//apple_ref/doc/uid/TP40014216-CH4-ID35)
>Swift provides default implementations of the == and === operators and adopts the Equatable protocol for objects that derive from the NSObject class. The default implementation of the == operator invokes the isEqual: method, and the default implementation of the === operator checks pointer equality. You should not override the equality or identity operators for types imported from Objective-C.