Issue 25 : Adding support for regex_replace and regex_match

[edmondop]

Solves #25

This pull requests add regexp_match and regexp_replace as defined in DataFusion signature.

Please note that the DataFusion signature is different from the PostgresSQL for what concerns the regexp_replace. In particular, the start and N parameters defined below are not supported

regexp_match('foobarbequebaz', '(bar)(beque)') → {bar,beque}

regexp_replace ( string text, pattern text, replacement text, start integer, N integer [, flags text ] ) → text

Replaces the substring that is the N'th match to the POSIX regular expression pattern, or all such matches if N is zero; see [Section 9.7.3](https://www.postgresql.org/docs/current/functions-matching.html#FUNCTIONS-POSIX-REGEXP).

regexp_replace('Thomas', '.', 'X', 3, 2) → ThoXas

[jacksonrnewhouse]

Looks good, just a couple small notes and rebasing on master.

[jacksonrnewhouse]

I'd clarify this is the Some(_) in the fourth argument case here.

[edmondop]

Fixed with 9889c37

[jacksonrnewhouse]

In general you don't need to have return types on your tests. Either it panics or it passes.

[edmondop]

Fixed with 9889c37

I am normally more used to work with functional errors rather than panics, that's why I naturally leaned on using results