MAX31856_CONFIG_REG ???

[AnHardt]

I know - this library is to abstract the #defines for the registers and bits in the registers away - the user should not need to use them.
However, the names for that should have the right IC-name in it.
All "MAX31856_*" have to be replaced by "MAX31865_*"
Here we are not dealing with the "MAX31856 Precision Thermocouple to Digital Converter
with Linearization" but the "MAX31865 RTD-to-Digital Converter".

And if the #defines are not thought to be used outside the library, should they be exported by the .h-file, or kept secret in the .cpp-file?

[caternuson]

Fixed with #30