version consistency

[calbaker]

One idea:

• make a fastsim-2 branch that contains vehicles matching the head of fastsim-2 in github.com/nrel/fastsim
• make a fastsim-3 branch ...
• whenever doing a new release of fastsim, e.g. v2.1.4, then make a tag in this repo with the same name that contains vehicle models that are valid for that same release