added python TennisGame5 and TennisGame6

[James-Ansley]

• ported games 5 and 6 from the Java version
• used similar formatting to the other python games

These have been really great! (even if some of them remind me of marking student assignments) I look forward to refactoring these versions as well.

[emilybache]

Thankyou! Glad I'm not the only one who gets to mark student assignments that look like this... :-)