Adding and removing multiple components from an entity.

Currently, [`Entry::add()`](https://docs.rs/brood/0.3.0/brood/world/struct.Entry.html#method.add) and [`Entry::remove()`](https://docs.rs/brood/0.3.0/brood/world/struct.Entry.html#method.remove) only support removing one component at a time. This means that the entity will have to be moved to a new archetype with every change if multiple changes are desired.

To account for this, `Entry::add()` and `Entry::remove()` should be modified to take multiple components. Additionally, a new method called `Entry::add_remove()` could be introduced which both adds and removes components at the same time.