[0.4]

Don't "nagle" in the reliable channel, require flush calls to ensure data is sent.
[API Change]: Change length limits in message channels to be uniformly u16 and use the type system to express maximum values rather than constants.
Fix panics in reliable bincode channel with messages near upper limit due to improper buffer size.
Document that all async methods are supposed to be cancel safe.

[0.3]

Fix the message_channels test to be less confusing, this is very important as it is currently the best (hah) example.
Make BufferPacketPool derive Copy if the type it wraps is Copy.
Simplify Runtime trait to not require an explicit Interval. Runtime::Delay wasn't even used prior to this, but it is the only timing requirement now and has been renamed to Sleep to match tokio 0.3. Neither tokio nor smol allocate as part of creating a Sleep / Timer, so having an explicit Interval is not really necessary to avoid e.g. allocation, and the way tokio's Interval works was not ideal anyway and we shouldn't rely on how it is implemented.

Correctness fixes for unreliable message lengths
Performance improvements for bincode message serialization
Avoid unnecessary calls to SendExt::send
Performance improvements and fixes for internal event_watch events channel.
[API Change]: Update to bincode 1.3, no longer using the deprecated bincode API
[API Change]: Return Result in MessageChannels async methods on disconnection, panicking is never appropriate for a network error. Instead, the panicking version of methods in MessageChannels only panic on unregistered message types.

Small bugifx for unreliable message channels, don't error with SendError::TooBig when the message will actually fit.