filter objects in scene to raycast, as raycaster is heavy

[minhhien1996]

After digging the docs, I found no option to filter objects in the scene to do raycasting. When my scene have some big mesh, the performance is not good. If I do the raycast manually, instead of

raycaster.intersectObjects(this.scene.children, true)

I will do

raycaster.intersectObjects(objectsShouldListenToEvent, true)

So I think an option such as func filterSceneChildren or array objectsShouldListenToEvent is good for cases like mine

[minhhien1996]

added a PR: #20

[jasonChen1982]

is a great idea

[minhhien1996]

@jasonChen1982 anything else needed for the PR to be merged? I added a method setObjectsToRaycast

[miguelfrmn]

Great idea!