Fixed python knights-on-chessboard solution + added python3 support
Fixed python knights-on-chessboard solution + added python3 support

mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview,mre/the-coding-interview