Formatting, utf8, and a few more cleanups

[nyurik]

When reviewing, make sure to enable "hide whitespace" in the diff.

• ran just fmt
• cleaned up the last remaining UTF8 strings as b"..."
• minor improvements to the doc examples
• made default timeouts to use Duration (they support const)
• Simplify exported namespaces - there is no point in having a multi-level exports when the entire API is just a few structs. Exported everything as root-level.
• Remove BinaryMessage -- it adds to mental load to look up that this type is an alias to Vec<u8>, which is a very common type to use in these scenarios. Better to be explicit that this is just a byte buffer, rather than hide it behind what appears to be a complex structure.
  • This made it possible for Clippy to note that in a few places it is possible to use &[u8] instead of &Vec<u8>

[thomasarmel]

Nice, thanks for your work and your nice advice!