include_file(file, res, content_type)
include_html(file, res)
include_md(file, res, format = NULL)
include_rmd(file, res, format = NULL)Content-type header in the response.output_format to rmarkdown::renderinclude_html will merely return the file with the proper
content_type for HTML. include_md and include_rmd will
process the given markdown file through rmarkdown::render and return
the resultant HTML as a response.