Provide API For Integrating Physics-Generated Bodies With Higher-Level Game Code

[ilexp]

Existing physics functionality like cutting tools or breakable bodies create new physics bodies as part of the simulation. However, for higher-level game code, these bodies do not exist. There should be an API that allows user code to be informed about the creation of these bodies, as well as the reason / context of their creation, so they can be integrated into the game properly.

First mentioned in this comment, issue #2