ObservableStore support

higher order store ObservableStore that allows observing action-chains to bring a concept of completion to reductive. To have completion in reductive, we would likely need to store the status of the side effect in a substate and then subscribe and observe changes to this substate, sometimes it might feel like an overkill, and we wished dispatch() would be able to return a Promise or Observable back, this is precisely what ObservableStore.observe() does, see usage.

Initial release

0.1.0

initial commit