Common interfaces for reading, writing, and observing changes in structured data

[DLehenbauer]

One seemingly simple thing that I think would benefit the JavaScript ecosystem in general are a set of standard contracts for observable data types that allow reactive systems to interoperate (e.g., a standard mechanism for an ObservableMap implementer to notify observers when keys are added, removed, or changed.)

@jack-williams and I have been slowly refining a set of such interfaces for Tiny-Calc, and I've made a first attempt at describing our thinking here.

I'd be interested in @taylorsw04, @CraigMacomber's thoughts/suggestions on the design (or improving the README. I feel like it sounds more complex than it is when I try to describe it.)