1.3.0

• add nodal-resistance script to compute the equivalent resistance of resistive networks
• add handling of unconnected circuits: Circuit.solve() will now raise UnconnectedCircuitError instead of crashing
• fix handling of CCVS and CCCS components to prevent crashing
• fix other minor bugs
• refactor: added the models and constants modules
• remove the State class and move its functionality inside the Netlist class
• expand testing and documentation