setter/getter

[jordens]

• more versatile than validation and with more concise/natural semantics, strictly a superset
• also fix mqtt tests that got unintentionally disabled by residual feature flags
• implements getter of #186

[jordens]

You mean in the case of a internal setter not doing some roll-back and returning Error::InvalidInternal? The onus is on the user to hold up contracts that ensure validity of their structs. They have the tools (a &mut self). I don't yet have a clear use case for internal setters/getters though. Supporting them just seemed natural.

[ryan-summers]

Yeah my main question was how miniconf-mqtt would handle it. Does it properly get forwarded up the error chain, or is it unwrapped?

Also, do we need to update miniconf-mqtt to use the getters?

[jordens]

It all gets returned cleanly. No unwraps. This is all transparent to miniconf-mqtt.