cmark: updated to 0.30.2

0.30.2

* Fix parsing of emphasis before links.
  Fixes a regression introduced with commit ed0a4bf.

* Update to Unicode 14.0 (data-man).

* Add `~` to safe href character set.

* Update CMakeLists.txt.  Bump the minimum required
  CMake to 3.7. Imperatively define output name for static library.

* Fix install paths in libcmark.pc.
  `CMAKE_INSTALL_<dir>` can be relative or absolute path, so it is wrong to
  prefix CMAKE_INSTALL_PREFIX because if CMAKE_INSTALL_<dir> is set to an
  absolute path it will result in a malformed path with two absolute paths
  joined together.  Instead, use `CMAKE_INSTALL_FULL_<dir>` from
  GNUInstallDirs.

(adam)