Update section 5 (CF-1.7)

[RosalynHatcher]

Additional checks:

5.6 Grid Mappings and Projections
Requirements:

• The type of the grid_mapping attribute is a string whose value is of the following form, in which brackets indicate optional text:

  grid_mapping_name[: coord_var [coord_var ...]] [grid_mapping_name: [coord_var ... ]]

• Note that in its simplest form the attribute comprises just a grid_mapping_name as a single word.

• Each coord_var is the name of a coordinate variable or auxiliary coordinate variable, which must exist in the file. If it is an auxiliary coordinate variable, it must be listed in the coordinates attribute.

• If present, the crs_wkt attribute must be a text string conforming to the CRS WKT specification described in reference [OGC_CTS].

• reference_ellipsoid_name, prime_meridian_name, horizontal_datum_name and geographic_crs_name must be all defined if any one is defined.

• If projected_crs_name is defined then geographic_crs_name must be also.

[RosalynHatcher]

In addition to the above:

• updated the list of valid grid_mapping_name attribute values.
• now checks the data types of the attributes of the grid mapping variable are as specified in Table 1 or Appendix F.