Classes
 ClassDescription
 b2DistanceJoint 1-D constrained system m (v2 - v1) = lambda v2 + (beta/h) x1 + gamma lambda = 0, gamma has units of inverse mass.
 b2DistanceJointDef Distance joint definition.
 b2GearJoint A gear joint is used to connect two joints together.
 b2GearJointDef Gear joint definition.
 b2Jacobian 
 b2Joint The base joint class.
 b2JointDef Joint definitions are used to construct joints.
 b2JointEdge A joint edge is used to connect bodies and joints together in a joint graph where each body is a node and each joint is an edge.
 b2MouseJoint A mouse joint is used to make a point on a body track a specified world point.
 b2MouseJointDef Mouse joint definition.
 b2PrismaticJoint Linear constraint (point-to-line) Angular constraint Motor/Limit linear constraint
 b2PrismaticJointDef 
 b2PulleyJoint The pulley joint is connected to two bodies and two fixed ground points.
 b2PulleyJointDef Pulley joint definition.
 b2RevoluteJoint A revolute joint constrains to bodies to share a common point while they are free to rotate about the point.
 b2RevoluteJointDef Revolute joint definition.