Update the protocols and transport subdirectories to the 2018 edition.
NB: The websocket transport cannot be moved to 2018 edition due to
websocket-rs's use of the keyword async as the name of a module.
* Add an Error associated type to transports
* Improve raw swarm a bit
* Rename map_other to map
* Use source() instead of cause()
* RawSwarmIncErr -> IncomingError
* remove tokio_current_thread tests
* Review changes:
Removed newline
Moved uds tokio test crate to top to avoid self and keep with convention of other test crates
Removed sleep from uds test and block until all futures are completed.
Refactor multiaddr crate.
- Remove `AddrComponent`. Instead `Protocol` directly contains its
associated data.
- Various smaller changes around conversions to Multiaddr from other
types, e.g. socket addresses.
- Expand tests to include property tests which test encoding/decoding
identity.
