NMEAGPS_cfg.h as a shared project configuration file #176
Description
I can't find a way to store NMEAGPS_cfg.h outside of my local NeoGPS library installation, due to the way it is hard-coded to be included from NMEAGPS.h.
Means I can't easily share my config with others working on the project. I've tried changing the include path to put my local copy of the file first, but this seems to break linking for me for some reason:
arduino-cli.exe compile --verbose -b esp32:esp32:ttgo-lora32 --build-properties "compiler.cpp.extra_flags=-I./config"
How about removing the include from NMEAGPS.h and giving a compile-time error if the user has not provided their own?