Add explicit signatures to some date autofunctions

Add explicit signatures to some date autofunctions

Because default_locale is eager, it generates misleading documentation when built (including on the site) as the doc will show the LC_TIME for the machine which built the doc.

An explicit autofunction signature fixes that and provides a more correct view of the signature.

An alternative fix would be for the LC_TIME value in the module to be a custom object with a repr of LC_TIME or something along those lines.

Fixes #542