Validate correct MI and CMI

[noamteyssier]

• Validate that the MI and CMI implementations line up with alternative forms of expression.
• Will also need to implement an empirical entropy function for these tests.

Mutual Information

Alternative Forms of MI Validate that the implemented form (double summation) is equivalent to the form H(X) + H(Y) - H(X, Y)

Conditional Mutual Information

Alternative Forms of CMI Validate that the implemented form (triple summation) is equivalent to the form H(X,Z) + H(Y,Z) - H(X,Y,Z) - H(Z)