Merge new subsetting code into framework

[jpolton]

Revisiting Steve Loch's subsetting edits for wrapped coordinates.

Merged in new develop.
Differences:

• moved calculate_haversine_distance from coast.py to general_utils.py

• Rewrite of coast/subset_indices_lonlat_box(self, lonbounds, latbounds). Now general_utils/subset_indices_lonlat_box(self, ww=np.NaN, ee=np.NaN, ss=np.NaN, nn=np.NaN) With new arguments.

• preserved old structure (not sure if this is good practise or not):

def coast/subset_indices_lonlat_box(self, ww=np.NaN, ee=np.NaN, ss=np.NaN, nn=np.NaN):
return general_utils/subset_indices_lonlat_box(self, ww=np.NaN, ee=np.NaN, ss=np.NaN, nn=np.NaN)

• Removed option of the cheap and dirty (and fast method):

    def subset_indices_lonlat_box(self, lonbounds, latbounds):
         """Generates array indices for data which lies in a given lon/lat box.
        Keyword arguments:
         lon       -- Longitudes, 1D or 2D.
         lat       -- Latitudes, 1D or 2D
         lonbounds -- Array of form [min_longitude=-180, max_longitude=180]
         latbounds -- Array of form [min_latitude, max_latitude]

         return: Indices corresponding to datapoints inside specified box
         """
         debug(f"Subsetting {get_slug(self)} indices within lon/lat")

         lon_str = "longitude"
         lat_str = "latitude"
         lon = self.dataset[lon_str].copy()  # TODO Add a comment explaining why this needs to be copied
         lat = self.dataset[lat_str]
         ff = lon > lonbounds[0]
         ff *= lon < lonbounds[1]
         ff *= lat > latbounds[0]
         ff *= lat < latbounds[1]

         return np.where(ff)

• Added some examples scripts:

example_scripts/subsetting_by_lon_lat.py (Requires no input data)
example_scripts/find_models_nearest_point.py (Requires input data)

[jpolton]

Actions:

• Check location of Haversine unit test

• Make unit test for subsetting by lat lon, based on the example script.

• Assess what to do with the new JSON files and example data.

• Assess how to edit the docs, if at all