Changes for connections from the web browser

[dkochmanski]

This set of changes introduces a new connection type :ASYNC that relies on Gray Stream interfaces. Moreover SLIME-NET-SEND anticipates that the connection may be associated with a websocket, and if that's the case we use a specialized function to send data.

With these changes I've managed to successfully connect from an image running inside the web browser to a shim server bridging SLIME and websockets.

[stassats]

And for some reason the CI breaks on CCL.

[dkochmanski]

I'll look into CCL tests not passing tomorrow. Thanks for reviewing these changes.