Async completion for void return calls

[guruofquality]

Use a form of windowing to speed up application of configuration settings for void return calls. This will be a non default option on the device constructor arguments:

A void return call is implemented like so:

    packer & args;
    ...etc...
    packer();

    SoapyRPCUnpacker unpacker(_sock);
}

Changes

A change in the SoapyRPCUnpacker with a shared state object will allow the unpacker to implement the windowed logic. The unpacker can decide to ack previous calls that were void 1) when the window length is reached, or 2) the call is a non-void return and we need the result:

    packer & args;
    ...etc...
    packer();

    SoapyRPCUnpacker unpacker(_asyncState, _sock);
}

Tasks

• [ ] Need optional args to set control window size (default 0)
• [ ] All unpacker calls need the state passed in
• [ ] Unpacker implements windowing algorithm
• [ ] Error handling when the async call returned an exception