Support grouping

[hedhyw]

Definition

(re)           numbered capturing group (submatch)
(?P<name>re)   named & numbered capturing group (submatch)
(?:re)         non-capturing group

Example methods

rex.Group.Define(...dialect.Token) GroupToken // `(tokens)`
rex.Group.Composite(...Token) GroupToken // `(a|b|c)`

type GroupToken struct {
   prefix   string
   tokens ...dialect.Token
}

WithName(name string) dialect.Token // prefix -> `?P<name>`
NonCaptured() dialect.Token  // prefix -> `?:`