Allow camera overide in opts

I've been trying to get the voxel-engine to accept a custom camera (ie: OrthographicCamera )
and it would seem that the Game prototype needs something like this:

this.camera = this.createCamera( opts.camera || false )

and createCamera needs changing like so:

Game.prototype.createCamera = function( customCamera ) {
  camera = customCamera || new THREE.PerspectiveCamera(60, this.width / this.height, 1, 10000)
  camera.lookAt(new THREE.Vector3(0, 0, 0))
  this.scene.add(camera)
  return camera
}

Does this seem like a good idea, or am I being stupid? If not then pull request to follow.

Start at Game.prototype.createCamera and the Game initialization that creates the camera; inspect how opts is passed and how THREE cameras are added to the scene. Confirm that a supplied OrthographicCamera is used while the default PerspectiveCamera behavior remains unchanged, then verify the resulting camera is added to the scene and positioned as expected.