Add hoistServer to HasServer

[phadej]

This is a refinement of an idea by @paf31.

I'll do documentation pass and add tests, if the idea is OK.

[alpmestan]

I quite like it. It's a bit of a shame that we'd have to define something identical for Client if we wanted to be able to operate on clients like this. Also, would we remove Enter altogether, with this? Maybe over the course of a few major releases, to give users some time to port their code. It might be nice to have a blog post for the first release that'll ship with this patch, to clearly and loudly document this breaking change.

[phadej]

I'd only deprecate enter, and keep it around for few major releases

[phadej]

@alpmestan, should I rewrite whole Enter section in the tutorial (i.e. only mention it existed?)

[alpmestan]

@phadej Well, we definitely want to explain the new stuffs. And maybe indeed add a little sentence or two that says "it replaces Enter, just do this to port your enter-based code over to hoistServer" ?

[phadej]

@alpmestan I'll merge this now and update tutorial in separate PR (as I guess there will be much more to review).

[alpmestan]

@phadej very good idea :)