ref #31, added stored procedure and output parameter support

Given the following PostgreSQL procedure:
    
    CREATE OR REPLACE FUNCTION testfunc(IN arg1 integer, OUT arg2 integer, OUT arg3 integer)
    RETURNS record AS
        'select $1 + 1, $1 + 2'
    LANGUAGE sql VOLATILE
    COST 100;

Sql2o can call it like this:

    final Integer inputArg = 20;

    OutParameter<Integer> p2 = new OutParameter<Integer>("outParam2", Types.INTEGER, Integer.class);
    OutParameter<Integer> p3 = new OutParameter<Integer>("outParam3", Types.INTEGER, Integer.class);

    sql2o.createProcedureCall("{call testfunc (:inParam1,:outParam2,:outParam3)}")
            .addParameter("inParam1", inputArg)
            .addParameter(p2)
            .addParameter(p3)
            .executeUpdate();

    int outParam2 = p2.getValue();
    int outParam3 = p3.getValue();

Any comments?