Add function to `engine` to remove an item from the index

[audy]

I would like to be able to remove things from a bucket.

I think the function should look like this:

engine.remove(id)
# what should it return?
# what should happen if `id` is not in the index?

So simple I might come back with a PR.

[pixelogik]

Sounds good. If you have time for it right now, would be awesome if PR. I am moving right now, chaoos