Add a SSHClient implementation using AsyncSSH. This is the first and
currently only class derived from SSHClient which implements
SSHClient.Cap.LogOutput, designed to consume and log command output
as it streams in. It felt like the lower hanging fruit not to do that
with Paramiko: Paramiko doesn't provide a native async API, so it
would need to spawn additional worker threads. I think.
Signed-off-by: Jan Lindemann <jan@janware.com>
