mkpage should integrate with Pandoc in server mode

[rsdoiel]

mkpage should integrate with Pandoc Server as a performance option. The problem in Pandoc in server mode doesn't support sub templates (partials) since it can only process the template passed to it in the POST. If mkpage could parse the template before making the post and render the sub templates then mkpage could be integrated with Pandoc server to provide a fast rendering experience without loosing support for sub templates.