Support asynchronous calls from language wrappers, e.g. Python wrapper

[grecinto]

We can support asynchronous from the language wrapper to the jsondb API. So they can implement in the language, some non-blocking call logic. Like async Python can consume it while doing something else.

And the jsondb API handler can easily use go channel & go routine to stream results as calls to B-tree comes in. Simple, 'can be added on V2 today, to make the Wrapper more appealing!