Add PostgreSQL Operator DDL Support

[LucaCappelletti94]

Adds support for CREATE OPERATOR, CREATE OPERATOR FAMILY, and CREATE OPERATOR CLASS statements.

Examples

-- CREATE OPERATOR with all parameters
CREATE OPERATOR < (
    PROCEDURE = cas_lt,
    LEFTARG = CAS,
    RIGHTARG = CAS,
    COMMUTATOR = >,
    NEGATOR = >=,
    RESTRICT = scalarltsel,
    JOIN = scalarltjoinsel
);

-- CREATE OPERATOR FAMILY
CREATE OPERATOR FAMILY integer_ops USING btree;

-- CREATE OPERATOR CLASS
CREATE OPERATOR CLASS int4_ops
    DEFAULT FOR TYPE int4 USING btree FAMILY integer_ops AS
    OPERATOR 1 <,
    OPERATOR 2 <=,
    FUNCTION 1 btint4cmp(int4, int4),
    STORAGE int4;