- Operations are now stored locally in memory. All operations are tied
to an HLC (Hybrid Logical Clock), making it possible to order them
concistently.
- Messages are handled in their `on*` methods, leading to a clearer
implementation.
- When a new peer joins, it asks a random peer for the list of
operations, and re-apply them locally.
- Messages types names have been updated to follow CamelCase, and to be
similar across the client and the server.
- Pass `sync=False` to `makeFeature` in the updaters, to avoid
generating duplicate operations on message retrieval.
