Create PigGame.java

/** A program that simulates 'Pig', a simple 2-player dice game. 
 *  Rules of the game:
 *      Players take turns. On each turn,  the player rolls the die. 
 *      1-If the player rolls a 1, they get no new points and their turn ends.
 *      2-If the player rolls a 2 through 6, they have 2 choices:
 *          ROLL AGAIN or
 *          HOLD. At this point, the sum of all rolls is added to the player's
 *              score and their turn ends.
 *      3-The first player to reach 100 points wins.
 *  The program designates one player as the user and the other player as the
 *  computer. On the user's turn the program shows both player's scores and
 *  each player's previous roll. The program allows the user to choose 'r' for
 *  roll and 'h' for hold.  On the computer's turn the program continues to roll
 *  until it has accumulated 20 points or they roll a 1.
 */