Report relative humidity (tested on TFA Airco2ntrol)

[julian-klode]

This adds relative humidity reporting on the TFA Airco2ntrol, I am not sure if other devices use the same entry point though. I think back in November when I wrote it I saw mentions of other entry points, but hopefully none re-use the same entry point for a different value...

[patrislav1]

Thanks for the PR. However, my unit (AIRCO2NTROL MINI) always reports humidity of 0%. Is it possible to auto-detect whether a unit supports it? We should either try to auto-detect it or make it a config option.

[GeoffreyFrogeye]

I can confirm this PR works as-is for me (I don't really know which unit I have).

@patrislav1 Maybe your unit supports it, but is sent under a different value? This article suggests at least some units, it is sent at 0x44 instead of 0x41.

Is it possible to auto-detect whether a unit supports it?

A humidity value of 0% is below the value range of the unit I have (20%-90% ; according to the label). It's a bit ugly, but we could use whether it's anything else but 0 to see if it's supported? Given it's used in cheap hardware, I wouldn't expect this to be reported properly by every device ; maybe some just don't wire things properly when it's not supported.