json: implement {manifest} template Property naming was borrowed from `hg files -Tjson`. We omit branch because, again, representation of branches in this template is wonky.

json: implement {shortlog} and {changelog} templates These are the same dispatch function under the hood. The only difference is the default number of entries to render and the template to use. So it makes sense to use a shared template. Format for {changelistentry} is similar to {changeset}. However, there are differences to argument names and their values preventing us from (easily) using the same template. (Perhaps there is room to consolidate the templates as a follow-up.) We're currently not recording some data in {changelistentry} that exists in {changeset}. This includes the branch name. This should be added in a follow-up. For now, something is better than nothing.

help: populate template functions via docstrings We do this for revsets, template keywrods, and template filters. Now we do it for template functions as well.