Allow Perl Compatible Regex

This is a feature request that includes similar issues such as #131.

In addition to solving the lack of case insensitive regex, allowing Perl Compatible Regex (PCRE) also adds more features, e.g. negative lookahead and single or multi line mode.
PCRE features can be consulted [here](https://perldoc.perl.org/perlre.html#Modifiers).

I'll submit a PR to address this.