* General code cleanup.
* All functions that return a characteristic or service have been renamed to have a `get` prefix to better represent their function.
* All functions that set a value have been renamed with the prefix `set` to better represent their functionality.
* Added an `bool notify` parameter to `setBatteryLevel`, which if `true`, will send a notification of the value to the peer.
* 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.
