get_total_score() added, get_average() and add_to_score() modified

add_to_score():
no use of score variable, if it is just the sum of the round_scores[]; it is be overdefined, and will make problems if u forgot to update one of it, and score != sum of round_scores[] 

get_total_scores():
adds up the scores in round_scores[]; making get_average(), and later methods easier

get_average():
usage of get_total_scores() and dividing by the length of the round_scores[]