Add Throws for exceptions to the docs

[304NotModified]

It's confusing that the docs talk about using .Returns, while we have .Throws (not sure from which version)

Not sure what I should do with the date in de post name. Should I update it?

(Please squash on merge PR)

Fixes #750

[304NotModified]

I dont know how to fix the compilation (because of the needed using)

[304NotModified]

I think I fixed it. But not sure if it's the best way.

[304NotModified]

I'm now confused, we have Throw and Throws, and both have the comments:

   /// <summary>Throw the specified exception when called.</summary>

and

<summary>Throw an exception for this call.</summary>

[dtchepak]

I'm now confused, we have Throw and Throws, and both have the comments:

   /// <summary>Throw the specified exception when called.</summary>

and

<summary>Throw an exception for this call.</summary>

Throw is part of WhenCalled, so it's meant to read as "when Xyz is called do ABC and throw DEF". When stubbing a call it reads "call ABC returns ABC / throws DEF".

[dtchepak]

Looks great, thanks for the doc updates! 🙇

Left some minor comments before we merge.

[dtchepak]

nitpick: missing trailing full stop.

See also [Callbacks](/help/callbacks).