Allow shutdown of underlying Socket

[matthid]

Description

We use the debugger in the integration-test suite (to test various stuff) and in order to make it work properly we need to shutdown the underlying socket.
To do this we need:

• Allow destroy zalmoxisus/remotedev#17
• Some changes in this Repository to use this new destroy function.

While technically this requires elmish/elmish#162
We have implemented it by "abusing" the init function in the following way: If init is called with a parameter of null we assume this is a program shutdown, which is good enough for our testing scenario.

This issue is a remainder and a starting point for discussion.
Is there interest in bringing these changes to this repository, maybe even depending on my fork of remotedev?

I spoke about this issue in the past here and here

[et1975]

Yes to both, I think. I haven't heard anything from Tim, but I guess we can move forward with the shutdown alpha release (thanks @MangelMaxime for catching that nonsense :)).

[matthid]

So you mean opening a PR for custom fork (or maybe even just bundling it) and the init abuse? :D

[et1975]

I mean let's implement the termination mechanism, as introduced in elmish v4 and the dependency on your fork seems ok to me. We don't include or reference JS dependencies, so it's just a matter of documenting it for the next major release, at least until the entire elmish stack is on Femto.

[et1975]

@matthid the master is ready to take these changes now.