Case insensitivite match/regular expressions

[kbrock]

Hello all,

Postgres supports case sensitive and insensitive operations.
Regular expressions match (~) currently defaults to case sensitive but match (LIKE) defaults to case insensitive.

The goal of this PR is to

1. Make case sensitivity explicit for match and regular expression match.
2. Introduce predicates matches_regexp and does_not_match_regexp.

I'd like it if both regular expressions and like match defaulted to case sensitivity, but that would change the def sql generated by postgres and I assume that is discouraged.

If you would like me to make both operators default to case sensitive (or case insensitive), let me know.

/cc @matthewd @tenderlove thoughts?

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[kbrock]

@tenderlove I can change this to have a different Arel operator for case insensitive operators instead of booleans. Just let me know.
Happy conference going.

[kbrock]

Wonder if this is a little related to #286
And ugh. Postgres uses different regular expression syntax. their SIMILAR TO uses % as a wild character, but the regular expression uses standard posix regexps .* as wild character.

I can split this PR into 2. Just ask that you state a preference around whether a) to default to case insensitive or sensitive and b) is case sensitive a boolean or a separate token?

Thanks

[tenderlove]

@kbrock tbh I'm totally fine with this. I'll merge it.