introduce cluster store

TODO

- [x] Rename Peer to Machine
- [x] Parse the new space separated bootstrap-config format
- [x] Ensure that the NodeName.ID()'s don't have collisions
- [ ] Generate initial cluster ID from a similar hash of the bootstrap-config
- [ ] Write documentation on static bootstrap

Given that `cluster.FindName(*name)` succeeded, I don't understand how it's ever possible for `cluster.Pick(cluster.FindName(*name).ID)` to fail.. can you give me an example?