• Removed pre from blocktags scanner. pre is handled separately
  in rule 1 and needn't be handled in rule 6.
• Added iframe to list of blocktags, as per spec change.
• Fixed bug with HRULE after blank line. This previously caused cmark
  to break out of a list, thinking it had two consecutive blanks.
• Check for empty string before trying to look at line ending.
• Make sure every line fed to S_process_line ends with \n (#72).
  So S_process_line sees only unix style line endings. Ultimately we
  probably want a better solution, allowing the line ending style of
  the input file to be preserved. This solution forces output with newlines.
• Improved cmark_strbuf_normalize_whitespace (#73). Now all characters
  that satisfy cmark_isspace are recognized as whitespace. Previously
  \r and \t (and others) weren't included.
• Treat line ending with EOF as ending with newline (#71).
• Fixed --hardbreaks with \r\n line breaks (#68).
• Disallow list item starting with multiple blank lines (commonmark/commonmark-spec#332).
• Allow tabs before closing #s in ATX header
• Removed cmark_strbuf_printf and cmark_strbuf_vprintf.
  These are no longer needed, and cause complications for MSVC.
  Also removed HAVE_VA_COPY and HAVE_C99_SNPRINTF feature tests.
• Added option to disable tests (Kevin Wojniak).
• Added CMARK_INLINE macro.
• Removed need to disable MSVC warnings 4267, 4244, 4800
  (Kevin Wojniak).
• Fixed MSVC inline errors when cmark is included in sources that
  don't have the same set of disabled warnings (Kevin Wojniak).
• Fix FileNotFoundError errors on tests when cmark is built from
  another project via add_subdirectory() (Kevin Wojniak).
• Prefix utf8proc functions to avoid conflict with existing library
  (Kevin Wojniak).
• Avoid name clash between Windows .pdb files (Nick Wellnhofer).
• Improved smart_punct.txt (see commonmark/commonmark.js#61).
• Set POSITION_INDEPENDENT_CODE ON for static library (see #39).
• make bench: allow overriding BENCHFILE. Previously if you did
  this, it would clopper BENCHFILE with the default bench file.
• make bench: Use -10 priority with renice.
• Improved make_autolink. Ensures that title is chunk with empty
  string rather than NULL, as with other links.
• Added clang-check target.
• Travis: split roundtrip_test and leakcheck (OGINO Masanori).
• Use clang-format, llvm style, for formatting. Reformatted all source files.
  Added format target to Makefile. Removed astyle target.
  Updated .editorconfig.