Fix a bug with scene switching causing crashes.

Signed-off-by: Robert Deaton <rdeaton@udel.edu>
Allow cameras backgrounds to be set in Scene's __init__, removing the need for on_enter.

Signed-off-by: Robert Deaton <rdeaton@udel.edu>
Remove on_enter, on_exit, etc. and replace them with events.
Support removing event handlers.

Signed-off-by: Robert Deaton <rdeaton@udel.edu>
Some todo updates.

Signed-off-by: Robert Deaton <rdeaton@udel.edu>
Update the concurrent example

Signed-off-by: Robert Deaton <rdeaton@udel.edu>
Move animations to sprites and (partially) update the animation example.

Signed-off-by: Robert Deaton <rdeaton@udel.edu>
Add support for key endings on event types.

Signed-off-by: Robert Deaton <rdeaton@udel.edu>
Update the animation example to use new input handling.

Signed-off-by: Robert Deaton <rdeaton@udel.edu>
Camera is now an optional argument to sprites, so reflect that in the forms code.

Signed-off-by: Robert Deaton <rdeaton@udel.edu>
Fix up aggregate sprites, add an aggregate example.

Signed-off-by: Robert Deaton <rdeaton@udel.edu>