Add coal plant controller to Hycon

[genevievestarke]

This PR adds a coal controller to Hycon. The controller takes in the day ahead LMP price, a plant status signal (0 if the plant is off, 1 if the plant is on), and a plant power bid curve.
If the plant is on, then the power set point is set according to the bid curve. If the plant is off, the power set point is zero.

To do:

• Code first draft of controller
• Code controller interface
• Add simple example from use case

[misi9170]

Thanks for working on this @genevievestarke ! Heads up that #100 makes some fairly significant changes to the Hercules interface, so we may need to revamp this somewhat once that is merged. We've been doing some testing with it and I think it's close, so perhaps I'll try to wrap up some last tasks on that today and try to get it on by early next week so that you can (hopefully) move forward unimpeded. Still, the logic for the coal plant controller shouldn't change.

I'm happy to talk you through #100 so that you know what's coming.

My other thought: is the logic you're implementing specific to coal, or is it likely going to hold for other types of thermal units, too?

[misi9170]

I've now merged #100, and it looks like there is a merge conflict on the Hercules interface, which isn't surprising. I can try to resolve that if you'd like @genevievestarke ?