Simplify "should throw"

[fsprojects]

Simplify "should throw"

[Evangelink]

@sergey-tihon Do you care about retro compatibility? (i.e. should I keep the old method and create a new one?). I am about to do this quick PR.

[sergey-tihon]

@Evangelink Yes we care about backward compatibility.
I think that we can support this feature in new FsUnit.Typed that is probably will be merged into FsUnit repo.

[Evangelink]

Ok cheers! I will have a look.

[Evangelink]

@sergey-tihon There is a shouldFail method line 36 (don't know how to link a portion of code) in your commit that already satisfy @tpetricek request.
(fun () -> failwith "BOOM!") |> shouldFail<exn>

Don't think it is worth doing a shouldThrow that will do the same thing (rename current method?). I can add a shouldFailWithMessage method that will also check the error message if wanted.

[sergey-tihon]

Released in v2.2.0-beta1