Updated Mechanics

Updated instantiation process to be encapsulated in newGame() function
which was previously startGame() fucntion. This will allow the game to
be reset easily once game logic is completed.

Updated playTurn() mechanics to prevent player from being able to
interact with AI's cards. Possible bug present where player is able to
play AI's down cards when there are no deck, hand, or up cards
remaining. However, AI is not currently developed to be able to test
this state.

Refactored g_drawNewCard() function to simplify code.