This code is somewhat messy because it has to work around the extreme
limitations of the xmldom window polyfill provided by Lemon.
- Updates the dependency on Beorn to 0.2.1 and adds a new one for
highlight.js at 11.8.0.
- Defines a wrapper build script to set up a transformation hook and
then dynamically run Beorn through an import.
- Updates .rsync-filter to exclude these new files.