WIP: Use threads to allow more than one connection

[yggdr]

I'd like to have the possibility to connect more than once to a monitor, so I tried a threading approach. This is still work in progress, I'd like someone who knows more about the gritty details of threads to have a look here. It seems to work well, but who knows what kind of bugs might lurk in the details.

[asvetlov]

@jettify ?

[jettify]

I like the idea, do not see any big issues with threads.

[achimnol]

This will be resolved by backporting aiomonitor-ng. :wink: