function Hinge(a, b, options) {
    this.a = a;
    this.b = b;

    Constraint.call(this, options);

    this.impulse = new Vec3();
    this.angImpulseA = new Vec3();
    this.angImpulseB = new Vec3();
    this.error = new Vec3();
    this.errorRot = [0,0];
    this.effMassMatrix = new Mat33();
    this.effMassMatrixRot = [];
}
A constraint that confines two bodies to the plane defined by the axis of the hinge.

@class Hinge
@extends Constraint
@param {Particle} a One of the bodies.
@param {Particle} b The other body.
@param {Options} options The options hash.