Pinning tex template version ? (Self-contained mode ?)

Right now, when rticles updates a template, it risks either breaking older markdown documents (for example, if the name of a header variable changes; see https://github.com/rstudio/rticles/pull/358) or changing the resulting pdf. This poses a challenge to reproducibility and stability.

Some of that could be ameliorated if instead of using the template.tex file that lives with the package, each article format copied the template.tex file to the root of the project at creation time and then used that file as template. That document is then shielded from updates to rticles. Of course, that also means that it also doesn't receive new updates (but if the user wants to update, they could create a new rmakdown file and then copy the the new template.tex, or perhaps there could be a command that does the update).

@cderv suggested that this could be an optional "self-contained" mode for advanced users. I don't know if this is possible or worth it.