Unable to resize Shapes

Apologies if this is the wrong repo, but it looks like `ncollide` is the proper one to add file this under. I have code that looks like this:

```rust
let mut body = RigidBody::new_dynamic(Ball::new(1.0), 1.0, 0.3, 0.6);
let handle = physics_world.add_rigid_body(body);
```

I would like to dynamically resize the object later on. The shape is getting stored as `ncollide::shape::ShapeHandle, nalgebra::Isometry3<{float}>>`. Since an `nalgebra::Isometry3` struct is being used to store the state of the shape, only translation and rotation can be updated. It appears that if an `nalgebra::Similarity3` struct were to be used instead, scaling could be set dynamically.