async and await will be keyword in python 3.7 -> syntaxerror

[Irmen de Jong]

See https://www.python.org/dev/peps/pep-0492/#deprecation-plans

will have to rename Pyro4.core.async to something else (and the keyword argument async as well)

Unfortunately, due to it being a syntaxerror, we cannot keep the old name around for older code
❗️ todo: update docs and examples to reference the change in name to asyncproxy/asynchronous