Add device capabilities and read humidity sensor

[mkalus]

Starting in FritzOS 7.25, the AVM FRITZ!DECT 440 can read the humidity of its surroundings. I have added the relevant code to include it in the library (although not in the command line tool - might be a bit longish and the 440 is not shown on thermostat temperature readouts anyway).

I also expanded the list of device capabilities I found in the official AVM documentation.

I would be happy if you accpted the pull request.

[codecov[bot]]

Codecov Report

Merging #237 (fb2160b) into master (4874fa4) will decrease coverage by 0.14%. The diff coverage is 50.00%.

@@            Coverage Diff             @@
##           master     #237      +/-   ##
==========================================
- Coverage   99.95%   99.80%   -0.15%     
==========================================
  Files         107      108       +1     
  Lines        2056     2062       +6     
==========================================
+ Hits         2055     2058       +3     
- Misses          1        4       +3     

Impacted Files	Coverage Δ
fritz/device.go	83.33% <40.00%> (-16.67%)	:arrow_down:
fritz/humidity.go	100.00% <100.00%> (ø)

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[mkalus]

Ok, might need to add a few trivial tests in device.go. Should I do that?