Expanded "Callables" chapter to include additional details. (#1723)

* Expanded "Callables" chapter to include additional details.

* Update docs/spec/callables.rst

Co-authored-by: David Salvisberg <[email protected]>

* Expanded "Callables" chapter to include additional details.

* Update docs/spec/callables.rst

Co-authored-by: David Salvisberg <[email protected]>

* Incorporated PR feedback from Jelle.

* Changed draft to indicate that `(*args: Any, **kwargs: Any)` in a `def` statement should be interpreted as `...`. Clarified that `...` can be used with `Concatenate` and explained how this is interpreted.

* Update docs/spec/callables.rst

Co-authored-by: Jelle Zijlstra <[email protected]>

* Incorporated feedback from Jelle.

* Incorporated suggested changes from Guido's PR review.

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Co-authored-by: David Salvisberg <[email protected]>
Co-authored-by: Jelle Zijlstra <[email protected]>

Author: 3 people