Doesn't scale with large amount of collections

[daltonpearson]

I'm trying to use mongoku with a database that has around 4000 collections (it's an odd topology I know). It works great on small databases running locally but it fails to load when I point it at a db with a lot of collections. There doesn't seem to be an issue open for this so I wanted to open this to discuss solutions. I'm willing to work on a PR to fix this but I thought I should ask for some input on if this is feasible in the first place before diving in.