Connect primary inputs and outputs.
When defining the constructor, calls are made to the I + O port
constructors. This expresses the connectivity between the ports
of the component and the connectors of the external environment.
This will have the effect of connecting the I/O ports with the
primary inputs and outputs of the circuit. Calling the
I/O port constructors also has the effect of placing the ports
in their respective linked lists. This is hidden from the user.
It is often useful to disguise the call to the port constructors
by using a CONNECT macro:
#define CONNECT(Port, Wire, name) Port(this, Wire, name)