This merge request implements polyglot (multi-language) binding documents. This is the first (and somewhat major) step along the way of supporting polyglot subplot documents. However as this branch is getting quite large, it would behoove us to merge this chunk first, and then proceed to support polyglot subplot documents themselves.
Some of the prep for the latter is contained in this branch, and it would be best to consider the work commit by commit. Some chore commits can likely be ignored. This is work towards #198 (closed) but does not pretend to fully fix that issue.