System now has addedToWorld and removedFromWorld methods. These can be overridden to listen for these events.
World now has entityAdded and entityRemoved signals (technically, a method which returns a signal). These can be used by a System to listen for specific Entity additions and removals. See README updates or test/world.js for examples.
Two main changes:
addedToWorldandremovedFromWorldmethods. These can be overridden to listen for these events.entityAddedandentityRemovedsignals (technically, a method which returns a signal). These can be used by a System to listen for specific Entity additions and removals. See README updates ortest/world.jsfor examples.