anchor: love.physics.newMouseJoint
  Create a joint between a body and the mouse.
  
  This joint actually connects the body to a fixed point in the world. To make it follow the mouse, the fixed point must be updated every timestep (example below).
  
  The advantage of using a MouseJoint instead of just changing a body position directly is that collisions and reactions to other joints are handled by the physics engine.
  joint = love.physics.newMouseJoint( body, x, y )
  body Body The body to attach to the mouse.
  x number The x position of the connecting point.
  y number The y position of the connecting point.
  joint MouseJoint The new mouse joint.