PCRE is now at end of life and is no longer actively maintained.
Lift the dependency to the next major version, i.e. PCRE2.
Implementation notes:
- Removed the pcre study option since:
"The new API ... was simplified by abolishing the separate "study" optimizing
function; in PCRE2, patterns are automatically optimized where possible."
- If asprintf() fails the content of the 'strp' variable is undefined.
Lets check the return value and return NULL upon error.
- Pattern and subject can straightforwardly be cast to PCRE2_SPTR since we
only work with 8-bit code units.
