• Updated to version 0.21 of spec.
• Added latex renderer (#31). New exported function in API:
  cmark_render_latex. New source file: src/latex.hs.
• Updates for new HTML block spec. Removed old html_block_tag scanner.
  Added new html_block_start and html_block_start_7, as well
  as html_block_end_n for n = 1-5. Rewrote block parser for new HTML
  block spec.
• We no longer preprocess tabs to spaces before parsing.
  Instead, we keep track of both the byte offset and
  the (virtual) column as we parse block starts.
  This allows us to handle tabs without converting
  to spaces first. Tabs are left as tabs in the output, as
  per the revised spec.
• Removed utf8 validation by default. We now replace null characters
  in the line splitting code.
• Added CMARK_OPT_VALIDATE_UTF8 option and command-line option
  --validate-utf8. This option causes cmark to check for valid
  UTF-8, replacing invalid sequences with the replacement
  character, U+FFFD. Previously this was done by default in
  connection with tab expansion, but we no longer do it by
  default with the new tab treatment. (Many applications will
  know that the input is valid UTF-8, so validation will not
  be necessary.)
• Added CMARK_OPT_SAFE option and --safe command-line flag.
  • Added CMARK_OPT_SAFE. This option disables rendering of raw HTML
    and potentially dangerous links.
  • Added --safe option in command-line program.
  • Updated cmark.3 man page.
  • Added scan_dangerous_url to scanners.
  • In HTML, suppress rendering of raw HTML and potentially dangerous
    links if CMARK_OPT_SAFE. Dangerous URLs are those that begin
    with javascript:, vbscript:, file:, or data: (except for
    image/png, image/gif, image/jpeg, or image/webp mime types).
  • Added api_test for OPT_CMARK_SAFE.
  • Rewrote README.md on security.
• Limit ordered list start to 9 digits, per spec.
• Added width parameter to render_man (API change).
• Extracted common renderer code from latex, man, and commonmark
  renderers into a separate module, renderer.[ch] (#63). To write a
  renderer now, you only need to write a character escaping function
  and a node rendering function. You pass these to cmark_render
  and it handles all the plumbing (including line wrapping) for you.
  So far this is an internal module, but we might consider adding
  it to the API in the future.
• commonmark writer: correctly handle email autolinks.
• commonmark writer: escape !.
• Fixed soft breaks in commonmark renderer.
• Fixed scanner for link url. re2c returns the longest match, so we
  were getting bad results with [link](foo\(and\(bar\)\))
  which it would parse as containing a bare \ followed by
  an in-parens chunk ending with the final paren.
• Allow non-initial hyphens in html tag names. This allows for
  custom tags, see commonmark/commonmark-spec#239.
• Updated test/smart_punct.txt.
• Implemented new treatment of hyphens with --smart, converting
  sequences of hyphens to sequences of em and en dashes that contain no
  hyphens.
• HTML renderer: properly split info on first space char (see
  commonmark/commonmark.js#54).
• Changed version variables to functions (#60, Andrius Bentkus).
  This is easier to access using ffi, since some languages, like C#
  like to use only function interfaces for accessing library
  functionality.
• process_emphasis: Fixed setting lower bound to potential openers.
  Renamed potential_openers -> openers_bottom.
  Renamed start_delim -> stack_bottom.
• Added case for #59 to pathological_test.py.
• Fixed emphasis/link parsing bug (#59).
• Fixed off-by-one error in line splitting routine.
  This caused certain NULLs not to be replaced.
• Don't rtrim in subject_from_buffer. This gives bad results in
  parsing reference links, where we might have trailing blanks
  (finalize removes the bytes parsed as a reference definition;
  before this change, some blank bytes might remain on the line).
  • Added column and first_nonspace_column fields to parser.
  • Added utility function to advance the offset, computing
    the virtual column too. Note that we don't need to deal with
    UTF-8 here at all. Only ASCII occurs in block starts.
  • Significant performance improvement due to the fact that
    we're not doing UTF-8 validation.
• Fixed entity lookup table. The old one had many errors.
  The new one is derived from the list in the npm entities package.
  Since the sequences can now be longer (multi-code-point), we
  have bumped the length limit from 4 to 8, which also affects
  houdini_html_u.c. An example of the kind of error that was fixed:
  ≧̸ should be rendered as "≧̸" (U+02267 U+00338), but it was
  being rendered as "≧" (which is the same as ≧).
• Replace gperf-based entity lookup with binary tree lookup.
  The primary advantage is a big reduction in the size of
  the compiled library and executable (> 100K).
  There should be no measurable performance difference in
  normal documents. I detected only a slight performance
  hit in a file containing 1,000,000 entities.
  • Removed src/html_unescape.gperf and src/html_unescape.h.
  • Added src/entities.h (generated by tools/make_entities_h.py).
  • Added binary tree lookup functions to houdini_html_u.c, and
    use the data in src/entities.h.
  • Renamed entities.h -> entities.inc, and
    tools/make_entities_h.py -> tools/make_entitis_inc.py.
• Fixed cases like
  [ref]: url "title" ok
  Here we should parse the first line as a reference.
• inlines.c: Added utility functions to skip spaces and line endings.
• Fixed backslashes in link destinations that are not part of escapes
  (commonmark/commonmark-spec#45).
• process_line: Removed "add newline if line doesn't have one."
  This isn't actually needed.
• Small logic fixes and a simplification in process_emphasis.
• Added more pathological tests:
  • Many link closers with no openers.
  • Many link openers with no closers.
  • Many emph openers with no closers.
  • Many closers with no openers.
  • "*a_ " * 20000.
• Fixed process_emphasis to handle new pathological cases.
  Now we have an array of pointers (potential_openers),
  keyed to the delim char. When we've failed to match a potential opener
  prior to point X in the delimiter stack, we reset potential_openers
  for that opener type to X, and thus avoid having to look again through
  all the openers we've already rejected.
• process_inlines: remove closers from delim stack when possible.
  When they have no matching openers and cannot be openers themselves,
  we can safely remove them. This helps with a performance case:
  "a_ " * 20000 (commonmark/commonmark.js#43).
• Roll utf8proc_charlen into utf8proc_valid (Nick Wellnhofer).
  Speeds up "make bench" by another percent.
• spec_tests.py: allow → for tab in HTML examples.
• normalize.py: don't collapse whitespace in pre contexts.
• Use utf-8 aware re2c.
• Makefile afl target: removed -m none, added CMARK_OPTS.
• README: added make afl instructions.
• Limit generated generated cmark.3 to 72 character line width.
• Travis: switched to containerized build system.
• Removed debug.h. (It uses GNU extensions, and we don't need it anyway.)
• Removed sundown from benchmarks, because the reading was anomalous.
  sundown had an arbitrary 16MB limit on buffers, and the benchmark
  input exceeded that. So who knows what we were actually testing?
  Added hoedown, sundown's successor, which is a better comparison.