Support for TrackballControls-like functionality

[MattFerraro]

I love all the extra functionality this library provides, but sometimes I need something more similar to TrackballControls. On its face this should be as simple as not keeping a constant camera up vector, but I'm sure that's easier said than done.

Still, is there any way this could be supported inside camera-controls?

[yomotsu]

Actually, TrackballControls is not compatible with OrbitControls.
camera-controls is a sort of OrbitControls and we can't add TrackballControls features.