Hostdb

I'm not 100% sure that this is complete, but I moved all of the hostdb stuff into its own package. I also switched from using an array that you went through in linear time every request to using a tree that only requires log time every request.

It's a weighted binary tree, but has no sorting. The tree helps with the weight, and there's a map to do lookups because we don't really care what order stuff is in, just that it's weighted. There are a few tests to make sure that the tree works alright.