function Manifold(lowID, highID, bodyA, bodyB) {
    this.lowID = lowID;
    this.highID = highID;

    this.contacts = [];
    this.numContacts = 0;

    this.bodyA = bodyA;
    this.bodyB = bodyB;

    this.lru = 0;
}
Class to keep track of Contact points.
@class manifold
@param {Number} lowID The lower id of the pair of bodies.
@param {Number} highID The higher id of the pair of bodies.
@param {Particle} bodyA The first body.
@param {Particle} bodyB The second body.