Direct Messaging

TODO

write space invaders
- can i use a message to find out if an object has an overlap with another?
  - what would we illuminate?
  - maybe just draw a different outline? (could be yellow like the beam)
- get it running in production mode
- then tweak debug mode until it's helpful and nice for this example
try out an example that's not inherently visual
come up with a better name for ReceiverDescriptor (it includes the sender, so it's not just describing receivers)