Try to find the Bullet physics engine

This module defines the following variables
BULLET_FOUND - Was bullet found
BULLET_INCLUDE_DIRS - the Bullet include directories
BULLET_LIBRARIES - Link to this, by default it includes
                   all bullet components (Dynamics,
                   Collision, LinearMath, & SoftBody)
This module accepts the following variables
BULLET_ROOT - Can be set to bullet install path or Windows build path