Closes #60. Implements binary message transport for API v3.

- Adds the `pkg/api/v3/message` package, the binary message transport reference implementation.
- Adds a router to route messages.
- Adds a multiaddr wrapper type to integrate multiaddrs with code gen.
- Updates code gen to support eliding names to allow for `message.Type` and `message.Unmarshal` instead of `message.MessageType` and `message.UnmarshalMessage`, etc (i.e. to avoid stuttering).
- Adds two error statuses for peer to peer error conditions.
- Removes the API batch interface in favor of transport mechanisms that batch requests.

Changelog: feature