create subfunctions for readRTD

[tdobrovolny]

Created subfunctions can be used for better cooperative multitasking because they do not use delay call.

[GasparQ]

Hello !

Would it be possible to merge this PR because this implementation would be very usefull ?
The automatic use of delay makes drop the rates if we use multiple temperature sensors.
If we want to fix it, we just need to rewrite your code and bypass your mechanisms.

Only one button to push ;)