add gps code to parse location sentence

[sisenegc]

• tested to work on gps chip and spits out something like "LNG -12210.495600, LAT 3725.627800, ALT 175.500000"
• wrote as a standalone thing, not sure where this should be put in the codebase currently
• TODO currently uses atof() from #include <stdlib.h>, because apparently "pico/stdlib.h" doesn't give right conversions for some reason (rewrite the function manually?)