Vehicle type discussion

[nreinicke]

When building out a new PHEV vehicle model in #33, we added a new Vehicle abstraction. Right now, there are two implementations of vehicles:

• SingleFuelVehicle: this represents vehicles that just take in a single fuel source (ICE, BEV, HEV).
• DualFuelVehicle: this represents vehicles that take in two fuel sources (PHEV).

This distinction works for now but we might need a more granular splitting of types since each of the vehicles represented in the SingleFuelVehicle will have different energy consumption behavior (and eventually energy addition behavior). For example, a BEV can return a negative energy value from the internal routee-powertrain model and this should be added back into the battery.

Perhaps we should build out a unique Vehicle implementation for each of the following:

• ICE (gas and diesel)
• BEV
• HEV
• PHEV

If we do this, there might be some shared code/behavior between some of these and so it might involve create a set of functions to share between these models.