mxcl/PromiseKit ? reverse-engineered prompt

Build me a Swift promise library like PromiseKit for Apple platforms and Linux, with good Objective C bridging too.

I want a clean, easy to use way to handle async work with chains like firstly, then, done, catch, ensure, and helpers for running multiple promises together. It should feel natural in Swift, but also work well from Objective C. Include the common conveniences for networking and Apple APIs so things like URLSession, location, and other platform specific tasks can be wrapped as promises.

Please make it work as a real reusable package, with support for Swift Package Manager and CocoaPods, and include solid tests and a few simple examples or playground style demos so it is easy to understand. If you need to check the latest Swift or Apple docs while building it, go ahead and look them up online.