Support Async in python API

[vicentebolea]

Why is this feature important?

asyncio is one of the hottest features of modern python. It allows you to write concurrent programs with minimum code. While in theory it is a fantastic way to enable seamless concurrent programming it depends on the procedures that perform the IO intensive routines to explicitly support python asyncio, this is to be awaitable.

What is the potential impact of this feature in the community?

This can be a killer feature for ADIOS2 since not many libraries support asyncio and supporting asyncio is highly precious in the python community. You could see many users to lean to adios2 rather than hdf5 since they can now do something else in their program while waiting for io in an adios2 file/IO object.

This is a feasible thing to do for us, we would probably implement this in the binding level (low-level) library since we need to support this with multithreading at the C/C++ level.