Add is_pseudolegal function

[wdotmathree]

• Implemented is_pseudolegal function to check if the cached TT move is legal before using it for an initial search in the future.
• Added a unit testing framework along to test future non search related changes for validity before deployment.
• Slightly revamped Makefile to streamline testing and debugging

TODO:

• Clean up Makefiles and make sure they are robust
• Improve unit testing coverage
• Switch to a different testing framework (I would like more direct feedback on test cases)

[kevlu8]

LGTM