modularizing BangleJS

Thanks! Yes, that looks really good, and it's nice clean separation.

I wonder whether for now, we even need libs/banglejs/hardware/barometer/bangle_barometer_impl.c and the ESPR_WEAK functions - I feel like we could probably just have that in jswrap_bangle_barometer.c. I feel happier in a way if we just define all the functions in every hardware implementation file, and the compile fails if eg someone misses banglejs_barometer_off_impl.

I like pulling out the repeated I2C initialise calls to arrays (did you ever see how much flash it saves?).