Parsing '[ (]([ (]([ (]([ (](...' takes quadratic time #285
Description
$ time py -c 'print("[ (](" * 10000)' | ./cmark >/dev/null
real 0m0.232s
user 0m0.030s
sys 0m0.000s
$ time py -c 'print("[ (](" * 40000)' | ./cmark >/dev/null
real 0m2.168s
user 0m0.000s
sys 0m0.045s
$ time py -c 'print("[ (](" * 80000)' | ./cmark >/dev/null
real 0m8.278s
user 0m0.016s
sys 0m0.046s
(Originally reported by @andersk for MD4C in mity/md4c#57 but applies to Cmark too.)