Infer dates from tags

[jaraco]

I really like what releases has done, and I'm considering adopting it in place of the technique I've developedcobbled together, which performs textual substitution on the .rst to inject links.

One feature I'd miss dearly in a transition to releases, however, is the date inference. Rst.linker will inject a timestamp based on SCM metadata (the date the tag was created). This approach allows a maintainer to simply publish the release version, but get release dates reflected in the published docs.

Perhaps releases could offer this behavior as an opt-in feature, maybe by default if no <date> is supplied in the release directive.