* fix: #200 Use `data()`/`size()` instead of `c_str()`/`length()`
* Reduce duplication, only allow template function in characteristic and remote value attr if the type is not a pointer (otherwise sizeof is useless). add appropriate notes
* clean up AttValue::setValue to remove unnecessary length parameter enabling requirement of non-pointer type
* Sets macros to allow compiling when Central role is enabled and Observer disabled, or Peripheral enabled and Broadcaster disabled.
* Adds a macro definition for CONFIG_NIMBLE_CPP_IDF to enable different include paths/functionality for IDF / Arduino.
