Add a simple event server

[vkovtash]

Hey Davin! Thank you for BlackHole, I really appreciate the work you've put into it.

I saw a feature request to add support for AU Plugins and I kinda agree that driver is not the place to host plugins. A simple user space plugin hosting app like HA Hosting or Element is a much better place.

However it would be nice to have a simple way to start AU hosting app when BH device is being used and stop the app when it's not needed anymore.

Hence this pull request, please consider merging it.

It adds a simple event server to the driver. Driver may communicate device activity statuses to other apps in user space that may be interested in them.

I'll send a separate pull request with a simple client app to keep the discussion focused.

Thank you!

[CLAassistant]

All committers have signed the CLA.

[devinroth]

Cool. I'll take a look soon.