Support Swift Package Manager

[peterboni]

Support developers using Xcode 11 and Swift Package Manager.

https://wwdcbysundell.com/2019/xcode-swiftpm-first-look/

[rosskimes]

Any plans for this now that Xcode 11 is out?

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. If this issue was overlooked, forgotten, or should remain open for any other reason, please reply here to call attention to it and remove the stale status. Thank you for your contributions.

[Jeehut]

This is not stale at all, SwiftPM is still not supported and we're at Xcode 12.3 already, so many are switching away from Carthage / CocoaPods, like we are doing right now. How can I remove stale from here?