Cosmetic reformat of GRIB/CF map.

This PR includes minor format changes to the `_grib_cf_map.py` file. There are **no** data changes.

These changes pave the way (eases the pain) for a following PR which incorporates the new GRIB/CF translations as generated by MetaRelate.

The summary of main format changes:
  * `CFname` to `CFName`,
  * `unit` to `units` (within the `CFName` namedtuple),
  * `:` to `:<space>` (addition of trailing space after colon in dictionary key/value pairs),
  * `"` to `'`,
  * `G2parm` to `G2Param`,
  * `G1Lparam` to `G1LocalParam`,
  * `GRIB1LocalConstrained_TO_CF` to `GRIB1_LOCAL_TO_CF_CONSTRAINED`,
  * `GRIB1Local_TO_CF` to `GRIB1_LOCAL_TO_CF`,
  * `CFConstrained_TO_GRIB1Local` to `CF_CONSTRAINED_TO_GRIB1_LOCAL`, and
  * `CF_TO_GRIB1Local` to `CF_TO_GRIB1_LOCAL`.