Canvas.update allows one arg. FPS is displayed nicer.

Because Canvas.update did not have any args, it could
not be used as an event handler. Now it can, which makes
attaching e.g. a timer to it much easier/cleaner.
Remove canvas.update from on_draw on all examples.

Use timer instead.
flake
add docs to canvas.update
Make examples use timer more effectively

Made some examples use 60 Hz
Make examples use Timer('auto', ...)
Better canvas.measure_fps
flake
Merge pull request #454 from almarklein/examples-60-fps

Let all dynamic examples run at 60 fps