Add clock.time() method

[tropxy]

Apparently there is no timer functionality on pgzero, for instance, to record how fast was player 1 to finish the level/game or even time played in general.

I am not sure about where to put this timer, but I guess that it could be added to the Actor class I guess...

[lordmauve]

This could be a new built-in. What would the API look like?

[tropxy]

I added a get_game_timer which returns the time elapsed since the start of the game in a readable string time format. One can also use other methods in the game_times.py script to do a time alive of an actor.

[lordmauve]

We should just add a method to get the current game time out of the clock, i.e. clock.time().