calc example -- PAST output

$ make
$ ./calc --target=past
> 3 + 4
"past" => PMC 'PAST::Op'  {
    <name> => "say"
    [0] => PMC 'PAST::Op'  {
        <pirop> => "add"
        [0] => PMC 'PAST::Val'  {
            <value> => 3
        }
        [1] => PMC 'PAST::Val'  {
            <value> => 4
        }
    }
}