Removed conditional constructions.
Added pressure as a state variable.

This is required to set the port pressure and to compute change in port pressure if the room is pressurized by the HVAC system.
Revised connections to fluInt.

This version checks correctly if the FFD is replaced by a replicator.
Corrected error in FFDExchange and added test case for FFDExchange.
Updated I/O conventions.
Implemented mass balance and propagated volume and initial conditions.
Declared yFixed and assigned values.