Add set_shank functionality and further clarify what shank spacing is in ghedt

[j-c-cook]

The following function needs to be completed. The function will set the shank spacing based on A, B or C options defined in Paul's MS thesis.

ghedt/ghedt/utilities.py

Lines 58 to 68 in 93d159c

	# TODO: Add `set_shank` functionality to utilities.py
	# def set_shank(configuration: str, rb: float, r_in: float, r_out: float):
	# raise ValueError('This function is incomplete.')
	# if configuration == 'A':
	# a = 1
	# elif configuration == 'B':
	# a = 1
	# elif configuration == 'C':
	# a = 1
	# else:
	# raise ValueError('Only configurations A, B, or C are valid.')

@mitchute mentions that the shank spacing s value in ghedt should be further clarified:

https://gist.github.com/mitchute/151522d67cdc21058ac523881f4e7957?permalink_comment_id=4049526#gistcomment-4049526