Add support for backslash escape in wikilinks

[digitalmoksha]

Adds support for using markdown backslash escapes in wikilink titles. So you can now use [ and ] in the title. For example [[Name \[of\] page]] or [[Name \[of\] page|https://example.org]]

Closes #470

[github-actions]

Command	Mean [ms]	Min [ms]	Max [ms]	Relative
./bench.sh ./comrak-33e2703	320.8 ± 1.0	319.4	323.2	2.89 ± 0.10
./bench.sh ./comrak-main	321.2 ± 1.9	319.1	327.7	2.90 ± 0.10
./bench.sh ./pulldown-cmark	110.9 ± 3.9	109.5	130.5	1.00
./bench.sh ./cmark-gfm	115.1 ± 1.3	112.9	119.7	1.04 ± 0.04
./bench.sh ./markdown-it	482.9 ± 3.7	476.1	490.2	4.35 ± 0.16

Run on Wed Sep 25 23:28:09 UTC 2024

[digitalmoksha]

Ran fuzzing and got a failure

cargo fuzz tmin all_options fuzz/artifacts/all_options/crash-05d3afe47da506bec3093ecbee89e067b36b6a4e

Reproduction input

[\0\0\0\0\0][[\u{2} \\y \\\X/\L2\ \\X\ ]]\ \\[][Es0<fRaM[Se\n-:\X/\\2\

I'll try and track it down tomorrow.

[kivikakk]

LGTM with one minor change (see comment), and escapes already roundtrip correctly in the CommonMark formatter!

[kivikakk]

Let's check if startpos != offset here, otherwise we'll append an empty span when a wikilink title ends in an escaped character.

[digitalmoksha]

Great point, thank you @kivikakk. Done.

[digitalmoksha]

After fixing the string overrun, I ran fuzzing for about 18 hours, no problems

[kivikakk]

Yes, LGTM!