textproc/cmark: update to 0.30.2, latest upstream
Release notes are at
https://github.com/commonmark/cmark/releases/tag/0.30.2
With some bugfixes and an update to unicode 14.0
Bump PORTREVISION on dependent ports, to force a rebuild;
this release changes some of the CMake & pkg-config machinery
and they should follow. (Also, potentially so-version bump)