added Body.setMass, Body.setDensity, Body.setInertia
removed engine.input, removed Engine mouse events, added MouseConstraint mouse events
changed Mouse.create to return as a plain object
removed redundant property
changed Grid.create to accept an options object
removed engine.broadphase.current, removed engine.broadphase.instance, changed engine.broadphase to refer to the broadphase instance, updated matter-tools
added docs for engine.timing.isFixed
added time scaling to Sleeping
changed Sleeping constants to be public (module level)
appease jshint