This brings about a major refactoring, to factor out common code for
regex compiles and matches.

failure messages.

after using pcre2_match_data_create_from_pattern() to create match_data.

This requires a test in configure.ac for whether UTF8 is enabled in
the PCRE2 lib against which the VMOD is built.

and recursion_limit, and test compile option use_offset_limit

note that I don't know at the moment how to test never_backslash_c

(and some notes about what will be needed to test options that are
not yet supported)

now with tests for allow_empty_class, anchored and bsr=unicode