Fix code gen for command overflow hooks

[bocchino]

• In the function prototypes and at the call sites, follow the pattern of the pre-message hooks. Don't include the command arguments. At the call sites, these are in serialized form and so are not available in typed argument form.
• Re-enable the call sites, which were commented out to get the code to compile.
• Update the unit tests.
• Update the version stamp to after v2.1.0.
• Re-generate the docs.

Closes #496.

[LeStarch]

@bocchino once merged, ready for a alpha?

[bocchino]

Yes, I will merge it and then make an alpha release.