Add HeatingAndCoolingSystem (singular) as child of HeatingAndCoolingSystems

[corymosiman12]

Under an auc:HVACSystem, there exists:

• auc:Plants/HeatingPlants/HeatingPlant ... etc.
• auc:DuctSystems/auc:DuctSystem
• auc:OtherHVACSystems/auc:OtherHVACSystem

However, under auc:HeatingAndCoolingSystems, there is no singular child element. The intention is to add the following:

• auc:HeatingAndCoolingSystems/auc:HeatingAndCoolingSystem

This would be a breaking change, but I believe makes sense from a consistency perspective.

@nllong @markborkum thoughts?

[markborkum]

@corymosiman12 It would be a breaking change for Audit Template, which uses the auc:CoolingSources, auc:HeatingSources child elements.

[nllong]

What is the motivation for this change other than to add consistency?