get_loads

Get loads of net in the top level module, return the leafs connections
Usage: @result = get_loads($net_or_pin, @options);
$net_or_pin: The net name or pin name that needs to get fanouts.
@options:
   -nonbuf: Trace the loads until none buffer 
   -bypbuf: Don't include buffer/inverter in the return array
   -hier: Loads cross hierarchies
   -fanend: Fanout endpoints, flops or ports
@result: A two dimension array. Each item has format of 'instance' and 'pin_name' if
         the load is leaf cell. Or 'port_name' and 'GOF_PIN_IN' 
@result = ([instance_0, pin_0],
           [instance_1, pin_1],
           [port_name, GOF_PIN_IN],
           ...
          )