Md4c

Changes:

* Make permissive URL autolink and permissive WWW autolink extensions stricter.

This brings the behavior closer to GFM and mitigates risk of false positives.
In particular, the domain has to contain at least one dot and parenthesis
can be part of the link destination only if `(` and `)` are balanced.

Fixes:

* [73](https://github.com/mity/md4c/issues/73):
Some raw HTML inputs could lead to quadratic parsing times.

* [74](https://github.com/mity/md4c/issues/74):
Fix input leading to a crash. Found by fuzzing.

* [76](https://github.com/mity/md4c/issues/76):
Fix handling of parenthesis in some corner cases of permissive URL autolink
and permissive WWW autolink extensions.

Changes:

* Changes mandated by CommonMark specification 0.29.

Most importantly, the white-space trimming rules for code spans have changed.
At most one space/newline is trimmed from beginning/end of the code span
(if the code span contains some non-space contents, and if it begins and
ends with space at the same time). In all other cases the spaces in the code
span are now left intact.

Other changes in behavior are in corner cases only. Refer to [CommonMark

Fixes:

* [58](https://github.com/mity/md4c/issues/58),
[59](https://github.com/mity/md4c/issues/59),
[60](https://github.com/mity/md4c/issues/60),
[63](https://github.com/mity/md4c/issues/63),
[66](https://github.com/mity/md4c/issues/66):
Some inputs could lead to quadratic parsing times. Thanks to Anders Kaseorg
for finding all those issues.

* [61](https://github.com/mity/md4c/issues/59):
Flag `MD_FLAG_NOHTMLSPANS` erroneously affected also recognition of
CommonMark autolinks.

New features:

* Add extension for GitHub-style task lists:


* [x] foo
* [x] bar
* [ ] baz


(It has to be explicitly enabled with `MD_FLAG_TASKLISTS`.)

* Added support for building as a shared library. On non-Windows platforms,
this is now default behavior; on Windows static library is still the default.
The CMake option `BUILD_SHARED_LIBS` can be used to request one or the other
explicitly.

Contributed by Lisandro Damián Nicanor Pérez Meyer.

* Renamed structure `MD_RENDERER` to `MD_PARSER` and refactorize its contents
a little bit. Note this is source-level incompatible and initialization code
in apps may need to be updated.

The aim of the change is to be more friendly for long-term ABI compatibility
we shall maintain, starting with this release.

* Added `CHANGELOG.md` (this file).

* Make sure `md_process_table_row()` reports the same count of table cells for
all table rows, no matter how broken the input is. The cell count is derived
from table underline line. Bogus cells in other rows are silently ignored.
Missing cells in other rows are reported as empty ones.

Fixes:

* CID 1475544:
Calling `md_free_attribute()` on uninitialized data.

* [47](https://github.com/mity/md4c/issues/47):
Using bad offsets in `md_is_entity_str()`, in some cases leading to buffer
overflow.

* [51](https://github.com/mity/md4c/issues/51):
Segfault in `md_process_table_cell()`.

* [53](https://github.com/mity/md4c/issues/53):
With `MD_FLAG_PERMISSIVEURLAUTOLINKS` or `MD_FLAG_PERMISSIVEWWWAUTOLINKS`
we could generate bad output for ordinary Markdown links, if a non-space
character immediately follows like e.g. in `[link](http://github.com)X`.

This was the last version before the changelog has been added.