Centralize weapon validity check into WeaponInfo.
Ensure a valid target in move.
Ensure valid targets in Selectable.
Convert Explosion to world coords.
Add WPos/WVec.LerpQuadratic to simplify ballistic calculations.
Redo husk particle physics using LerpQuadratic.
Improve Leap behavior:

* Configurable jump speed.
* Configurable jump angle.
* Configurable attack sound (uses weapon report).
* Don't accidentally eat tanks.