Refactor HashTable private members

Change: private members adhere to underscore convention.
Refactor Human private members

Change: private members adhere to underscore convention.
Refactor Zobrist private members

Change: private members adhere to underscore convention.
Refactor Game private members

Change: private members adhere to underscore convention.
Refactor Perft private members

Change: private members adhere to underscore convention.