Document calling a command as a regular function

[kdeldycke]

Document an old open issue on how to call a command as a regular function.

Closes #1054.

[davidism]

I'm not sure I want to document calling callback directly. It feels like an internal implementation detail. I think the other strategies are sufficient.

[Rowlando13]

If it's an implementation detail we should document as private and deprecate public api in the next feature release.

[kdeldycke]

I'm not sure I want to document calling callback directly. It feels like an internal implementation detail. I think the other strategies are sufficient.

Removed in https://github.com/pallets/click/compare/18924fda3f3369c060ca12b53ba60aba1300def5..bb86cdea6e83bc8e2711290eeffb4c8654baa7a3 .

Now what do you think of @Rowlando13 proposition to make it a private method and deprecate it?

[davidism]

We don't need to go that far, it's fine that it's accessible as "the thing the command calls", but we don't need to promote it as a thing to call directly.

[kdeldycke]

We don't need to go that far, it's fine that it's accessible as "the thing the command calls", but we don't need to promote it as a thing to call directly.

OK good, so this PR is ready to be merged upstream! :)