## Solution
`Commands.remove` and `.retain` (because I copied `remove`s doc)
referenced `EntityWorldMut.remove` and `retain` for more detail but the
`Commands` docs are much more detailed (which makes sense because it is
the most common api), so I have instead inverted this so that
`EntityWorldMut` docs link to `Commands`.
I also made `EntityWorldMut.despawn` reference `World.despawn` for more
details, like `Commands.despawn` does.