bidirectional stream flows
documentation (add links to http://www.physiolibrary.org and to user guide)
better backup for default file Dymola\insert\displayunit.mos
rename HydraulicResistanceConst to HydraulicResistanceToConductanceConst
add HydraulicElastanceToComplianceConst
add unit "mmHg/ml"
Fix: ElasticVessel problem with external inputs