MIME: added text/markdown type. Added text/markdown type for the ".md" and ".markdown" extensions (https://www.iana.org/assignments/media-types/text/markdown). Additionally, text/markdown is added to the default charset_types list of the charset module, making it easier to provide the "charset" parameter, which is defined as REQUIRED for text/markdown. Prodded by Andrea Pappacoda, http://freenginx.org/pipermail/nginx-devel/2024-August/000486.html