Support for POSIX regular expression

[luigi-riefolo]

What would you like to be added: Hi, first of all let me say thank you to all of you that created this project. Definitely one of the best ones I've seen in years.

I'll soon be starting using this project for work, but we have an additional requirement: support for POSIX regular expression as described here (9.7.3): https://www.postgresql.org/docs/9.3/functions-matching.html

Why is this needed: It can extend the support for pattern matching.

I'll be more than happy to work on a PR if this request gets approved.

[dosco]

Would love to have that feature added in. We have support for similar and not_similar adding posix regex should very similar you can jus follow that code path.

[luigi-riefolo]

@dosco I'll take that as a yes then. I'll start tomorrow.