Add macOS support.

[RyPoints]

Already works. Already been using it. Just needs to be added to the podspec.

[RyPoints]

Ah, looks like because of updates with UIImage/NSImage you also need the changes here: https://github.com/RyPoints/DataCache/commit/be9836986e337977947b5a9fe6c35a7968ac697c

You could just #ifdef a little in DataCache.swift and support macOS though.

[huynguyencong]

But you have changed the code to Cocoa and NSImage, it won't work on iOS anymore, will it?

[RyPoints]

Yeah, it won't like that. That's just for me on macOS. You can easily support both though via wrapping my code and using:

#if os(OSX)
    import Cocoa
#elseif os(iOS)
    import UIKit
#endif

[huynguyencong]

This supports macOS but doesn't support iOS. I will close it.