Publish Expect module as it's own Nuget package

[ZaymonFC]

The Expecto.Expect module is my favourite assertion library but changing the test runner is not currently feasible.

It would be really nice to solely consume Expect as a dependency.

[haf]

There's a cost to everything, including breaking things up. There's a cost for learning to pull down both Expecto.Core and Expecto.Expect via the meta-package Expecto. It lowers cohesion ever so slightly (and even more if you count Expecto.Diff) and decreases the synergy effect of people using both Expect and the "runner". I had this argument twice in Suave; one for adding MSFT's cross-web-server API (which was a cunning trap) and one for separating out the API from the server; was forked instead into Giraffe.

Based on this; I don't want to pay for this feature out of my spare time, but I see the value in it. If you value it enough to sponsor me at the professional level https://github.com/sponsors/haf for it, I'll make it happen; otherwise, I prefer cohesion over less coupling.