code: def nearest_loc_obs(self, lat, lon):
          
          sitelist = self.loc_observations(SITELIST)
          sites = parse_sitelist(sitelist)
          site = get_nearest_site(sites, lat, lon)
          return self.loc_observations(site)
docs: Work out nearest possible site to lat & lon coordinates
          and return observation data for it.
          
          lat:    float or int.  Latitude.
          lon:    float or int.  Longitude.