Render output with bookdown

[peterdesmet]

Mainly because:

• We want to be able to run several Rmd in series
• We don't want all the site assets bundled up in the html
• We want to output to /docs without the (function(input_file, encoding) { rmarkdown::render(input_file, encoding = encoding, output_file = paste0("../docs/",sub(".Rmd", ".html", basename(input_file))))}) hack

[peterdesmet]

This has been done long time ago, see: https://trias-project.github.io/unified-checklist/