Basically, every #get method accepts start_key, but get_indexed_slices accepts key_start. I know this makes sense (key_count, key_start, key_finish), but it isn't consistent.
I agree. Can you submit a pull request that supports both and updates the docs? I'm planning to push a new release this weekend and I'd love to include this. Otherwise I'll probably won't get to it until next week.
Sorry for the delay, working on this now.