Clean up `src/fgen/templates`
The problem
As a developer, I want to add support setters and methods that return different types. There isn't enough structure to src/fgen/templates, so it is hard to see where new pieces need to be added or make sense of what is going on.
Definition of "done"
-
fixed up naming throughout the directory -
made Fortran and python structures more symmetric so it is easier to see what is going on and how things map to each other -
docs explaining how these templates are set up