Support missing pcre patterns

[quasilyte]

• [x] lookahead / lookbehind (?=re) (?!re) (?<=re) (?<!re)
• [x] atomic groups (?>re)
• [x] alternative named group syntax (?<name>re)
• [x] alternative named group syntax (?'name're)
• [ ] recursive sub-pattern call (?n) (?+n) (?-n) (?R) + named variants
• [ ] things like (*PRUNE) and (*ACCEPT)
• [ ] escapes like \cK
• [ ] g/k backreferences gn g{n} g{+n} g{-n} + named variants

https://github.com/google/re2/wiki/Syntax https://www.debuggex.com/cheatsheet/regex/pcre