This command has 2 subcommands: `make` and `receive` to make a new call or wait for one.
When call is in progress, a window will be created to show incoming stream and local
feedback, and a text UI is available to (un)mute audio or video, and hang up.
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it may be necessary to run some async cleaning method (e.g. if bridge is needed), this new
method handles async cleaning method, and will be called when `SystemExit` is used, or if
`a_quit` is called explicitely.
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