* Do not copy with allocations.
* Remove unused DeepestNotMeContactTestResultCallback.
* Avoid using pointers which should not be nullptr.
* Move constructors implementation to headers.
* Move types defined in .cpp are to unnamed namespace.
* Comment unused arguments.
* Avoid C-style casts.
imprecision issue with projectile collision detection.
Simplify the mechanics: manage hits in one spot.
Give magic projectiles a collision shape similar in size to their visible
model.
Rename the 2 convex result callback to clearly state their purpose.
