Joint API and joint motors improvements

src/dynamics/rigid_body_set.rs

@@ -121,7 +121,8 @@ impl RigidBodySet {
     }
 
     /// Insert a rigid body into this set and retrieve its handle.
-    pub fn insert(&mut self, mut rb: RigidBody) -> RigidBodyHandle {
+    pub fn insert(&mut self, rb: impl Into<RigidBody>) -> RigidBodyHandle {
+        let mut rb = rb.into();
         // Make sure the internal links are reset, they may not be
         // if this rigid-body was obtained by cloning another one.
         rb.reset_internal_references();