GridLAB-D deltamode

[trevorhardy]

Deltamode allows GridLAB-D to simulate at timescales smaller than 1 second. HELICS support in GridLAB-D support entering and leaving delta mode and having an example that demonstrates this. Ideally, the example would start out in QSTS, have an event that triggers delatmode (likely a transient of some kind) and then return to QSTS once the transient has ended.