Allow for specifying custom fragments to be included in head element #71
Description
For the En-ROADS Technical Reference, we need to be able to customize the <head> element of certain pages to allow for embedding special components on a per-page basis. I'm proposing to extend docs-builder to support frontmatter in the source Markdown files.
For example, if you include the following frontmatter:
Then docs-builder will look for a file called fragment-example.html, and it will inject the content of that file into the <head> element of the generated HTML page.