things to do (eventually.)  patches are welcome, thanks!

 - support for using client-side certificates.
 - `location' support for blocking certain sub-trees (or maybe even
   location-dependant proxying!)
 - try to extract the page title (need a separate per-request buffer.)
 - `listen' directive: allow to listen on (multiple) sockets, be UNIX
   or TCP ones.
 - extend to support gopher and/or spartan?
 - simplify process IPC: proc.c is cool but provides more than we need;
   there's no web of process that communicates between each others, just
   a parent and (some) proxy processes.
 - make the build from the tarball works without building `template'.
 - generate ids for headers for ease of linkability;
   https://docs.gitlab.com/ee/user/markdown.html#header-ids-and-links
 - link to generate a RSS/Atom feed for the current page