Add utility to build turbine yaml from absolute power, thrust curves

[misi9170]

Users have reported that often turbine data is provided in terms of absolute power (often paired with thrust coefficient) per wind speed.

This utility converts tables of wind speed coupled with absolute power and/or absolute thrust to a turbine input yaml file, containing the power and thrust coefficient tables.

Checklist:

• Code runs
• Tests built
• Tests pass
• Example to demonstrate usage. Is this needed/warranted?

[misi9170]

I've altered the functionality a little to have the utility return a turbine dictionary (which can be passed to turbine_type in a fi.reinitialize() call), and optionally create a matching turbine yaml file (if file_path is specified).

I've also added an example.

[misi9170]

@rafmudaf some of this functionality (but not all of it) will become redundant when we switch to an absolute power curve in 4.0. I think there will still be useful aspects though. I think this could be put in for 3.6 as is, or if you'd like we can wait until 4.0/4.1 and I can revamp it a bit at that point.