Fix linter

[nritsche]

Closes #159

[jrs65]

Thanks!

This all looks like it should work fine to me now. However, I think the use of pathlib in here could do with straightening out. There's a bunch of places where pathlib methods are being called like functions, e.g. Path.is_absolute(f) rather than f.is_absolute(), and where Path.joinpath(a, b) is being used instead of a / b. I've made a few suggestions, but they're not exhaustive so you'll probably need to look through more carefully.