Refactor to use pathlib

[csatt]

This Issue was brought to my attention by the "refurb" tool. Among many others, refurb makes the following suggestions:

[FURB104]: Replace os.getcwd() with Path.cwd()
[FURB141]: Replace os.path.exists(x) with Path(x).exists()
[FURB144]: Replace os.remove(x) with Path(x).unlink()
[FURB150]: Replace os.makedirs(x) with Path(x).mkdir(parents=True)

"Path" is referring to the Path class of the pathlib module. The pathlib module was introduced in Python 3.4, and is a more "modern" way to deal with the filesystem using objects instead of strings. There are many articles about why new code should use pathlib instead of the os module, and many advocate refactoring existing code. There's a pretty good counterargument, which is, "if it ain't broke, don't fix it." But I have generally tended to try to incrementally improve the IV Swinger 2 code toward adhering to Python coding best practices, where feasible.

The four cases that refurb calls out are just scratching the surface. There are many other cases of os module functions that can and should be refactored to use pathlib. This Issue will track these changes.

I will file another Issue later to address all of the other refurb suggestions not related to pathlib.