Create example using async time request

[trevorhardy]

Yet another feature that doesn't have an example: helicsFederateRequestTimeAsync. This features allows a HELICS integrator or modeler to make a non-blocking time-request, execute other arbitrary code, and then "complete" the call by using helicsFederateRequestTimeComplete. We need to add an example showing how this API works, maybe doing something silly like just adding logging messages during the non-blocking portion of the call?