Added subset and superset operations for sets

[joente]

Description

Added support for the following set operations:

Operation	Description
<= (is subset)	Determines if a is a subset of b.
<(is proper subset)	Determines if a is a proper subset of b (subset, but not equal).
>= (is superset)	Determines if a is a superset of b.
> (is proper superset)	Determines if a is a proper superset of b (superset, but not equal).

Type of change

• [x] New feature (non-breaking change which adds functionality)

How Has This Been Tested?

• [x] Update operations tetsting

Checklist:

• [x] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation
• [x] New and existing unit tests pass locally with my changes