Update to 2.2.4. From the changelog:

1. (bugfix) when splitting a line, null terminate the new line; also
  don窶冲 inherit the dle from the previous line
2. (bugfix) fix the broken footnote code; allow multi-paragraph
  footnotes, not just one line of footnote.
3. (feature) support github checkbox list items (static configuration option)
  a. --github-checkbox does the checkbox with html check entities
  b. --github-checkbox=input does them with html <input> elements (set
      to disabled so that people can窶冲 check and uncheck willy-nilly)
4. (feature) on systems that support it, use the 窶賄estructor窶�
  attribute on mkd_shlib_destructor() so it will run automatically when
  the library unloads.
5. (feature) add --cxx-binding option to configure.sh to generate a
  mkdio.h that窶冱 got an extern "C" wrapper around it.
6. (tweak)delete HGROUP from the list of html5 elements, because the w3c
  working group decided to punt it

The bugfix for not null-terminating a split line was reported by Github
user fCorleone, who was running a input mangler program (afl) to stress
discount by feeding random garbage to it. It saw that the splitline()
function (used when breaking out embedded chunks of html) was not
null-terminating the split line chunks, and was throwing errors on that.
(this is something that clang on modern macos catches if you use the
-fsanitize=address option.)

I never actually use footnotes, so I窶囘 been running for about a decade
assuming that footnotes were one or maybe two lines, but github user
somasis pointed out that this was wrong wrong wrong! Ooops; at least it
was fixable w/o much pain and suffering.

HGROUP was caught by github user Crypto-Anarchist in their own branch of
discount, so I cherry-picked that changeset and pulled it back into the
mainline discount.

(schmonz)