change regex API to use Semigroup flags, defaults false

[jamesdbrock]

the default regex should provide no configuration? You can then provide a regexWithFlags version, and partially apply it for the default case regex = flip regexWithFlags (unicode <> dotAll).

On reflection, let's just have all of the flags set to false by default, maybe that’s less surprising.

Originally posted by @jamesdbrock in #153 (comment)