Move generated files out of main branch, instead generate them via a workflow and put them into gh-pages branch

[fingolfin]

A nicer approach would be to remove all these generated files from this branch in the repository, and instead add a CI workflow which generates everything (SVG, pngs, etc. in a well-defined CI environment) and published them as a website in the gh-pages branch.

Originally posted by @fingolfin in #1 (comment)