mdq: find specific elements in a md doc

This tool made me chuckle because I've always thought one of the cool things about Markdown files is that they have a structure to them per se, and you can use that structure to create things like a table of contents, or build programmatic content off of. For example, mdq would make it very easy for me to generate an index for each issue of the Weekly Thing and let you jump to each specific section or link. Or even just do a find on a directory with all the issues, pipe them through mdq and use simple wc -l to answer questions like "How many links did I share in 2024?". Cool stuff!