Support for timed/bursty TX + Receive error types

[JohnnyGOX17]

• Allows timed and burst transmit operations via TransmitMetadata builder and new send() TX method (should fix Timed sends currently not supported #13 ). Verified running on my Ettus B205mini on macOS, which also fixed issues I was seeing with packetized transmit modes.
• Exposes ReceiveErrorKind types to allow receiver logic to handle/match returned status from receives.
• Minor clippy fixes.

I updated the uhd changelog with a version bump to 0.4.0 but I can change that to unreleased if you'd prefer.