• Properly indent block-level contents of list items in man (#258).
  This handles nested lists as well as items with multiple paragraphs.
  The change requires addition of a new field block_number_in_list_item
  to cmark_renderer, but this does not change the public API.
• Fix quadratic behavior when parsing emphasis (#389, Nick
  Wellnhofer). Delimiters can be deleted, so store delimiter positions
  instead of pointers in openers_bottom. Besides causing undefined
  behavior when reading a dangling pointer, this could also result
  in quadratic behavior when parsing emphasis.
• Fix quadratic behavior when parsing smart quotes (#388, Nick Wellnhofer).
  Remove matching smart quote delimiters. Otherwise, the same opener
  could be found over and over, preventing the openers_bottom
  optimization from kicking in and leading to quadratic behavior when
  processing lots of quotes.
• Modify CMake configuration so that the project can be built with
  older versions of CMake (#384, Saleem Abdulrasool). (In 0.30.0,
  some features were used that require CMake >= 3.3.) The cost of this
  backwards compatibility is that developers must now explicitly invoke
  cmark_add_compile_options when a new compilation target is added.
• Remove a comma at the end of an enumerator list, which was flagged
  by clang as a C++11 extension.
• make_man_page.py: use absolute path with CDLL. This avoids the error
  "file system relative paths not allowed in hardened programs."
• Include cmark version in cmark(3) man page (instead of LOCAL).