Transactions should probably be observables

[nhunzaker]

For background, whenever an action is pushed into Microcosm via app.push, it runs coroutine on the value returned from the action. There are 3 states returned from coroutine: progress, fail, and done. This is very similar to how Observables work, and I would love to expose interoperability with transactions to libraries like Rx. At the very least, use an already existing pattern that is well established in the community.

If we did this, is it feasible to make it compliant with RxJS? https://github.com/Reactive-Extensions/RxJS. We have our own scheduler, dispose strategy, and observation pattern - would it be too hard do this? How could we mitigate as many breaking changes as possible?