Add #56

[Tymewalk]

This seems like it should be a one-commit thing although I'm going to follow the policy on making new pull requests for things that could break programs.

So, anything that's been left out?

[Tymewalk]

Glad I made a pull request, as it turns out this just messed up isVisible().
OK - can anyone else think of what else should be done here?

[Tymewalk]

I just checked, no examples use this. I'll merge this soon once I make sure that Slither still works.

[Tymewalk]

Traceback (most recent call last):
  File "slither/examples/turnAndMove.py", line 13, in <module>
    slither.registerCallback(pygame.QUIT, handlequit) # This uses the direct call form
NameError: name 'pygame' is not defined

I'll see what I can do to fix this.

[Tymewalk]

Oh, that's just a missing import pygame in the example, not anything to do with Slither.
I'll merge this since nothing bad happened.