Create a library of FFD operations

[ewu63]

Write generic FFD functions and put them as a library. Make them customizable, so that people can import instead of writing their own twist functions etc. every time they want to run an optimization.

List of functions:

• twist
• shape
• chord (w/ and w/o Yehudi)
• span
• sweep
• dihedral
• tail rotation?

[gawng]

This might be more useful to have in the pygeo documentation as potential functions to copy-paste since sometimes people have very particular ways of doing their DVs. What do you think about that? I definitely think some sort of standardized way would be good to have as reference.

[ewu63]

I think if there's a way to standardize things, and make the functions flexible enough that they can be used by everyone, then they should be shipped with pyGeo and people can just use them directly. If this is not possible for whatever reason then documentation would be the way to go, but I think it's less helpful.

Function factories can be made by either nesting functions, or I guess a more pythonic way would be to use decorators.