Better naming conventions: What is `operations.py`?

[caten2]

The class Relation is defined in src/relations.py, so one would imagine that the class Operation would be defined in src/operations.py, but this is not the case. The current operations defined in src/operations.py are arithmetic operations use in more basic examples/testing for the discrete neural net setup, and these should be moved somewhere like src/arithmetic_operations.py. Meanwhile, src/operations.py should contain the Operation class.

[caten2]

I think I'm going to make this change before I merge the path_architecture branch I've been working on.

[caten2]

I made some name changes along these lines.