Fixes for grid_latitude/grid_longitude standard names
Fixes for grid_latitude/grid_longitude standard names

Removes check for grid_mapping when attempting to find rotated lon/lat
coordinates.  Also allows other units equivalent to "degrees" in
UDUNITS, but lacking east/north components to be used.

Candidate for #508

Also fix improper usage of "it's" in comments. :)

aodn/compliance-checker,DanielJMaher/compliance-checker,lukecampbell/compliance-checker,ocefpaf/compliance-checker,ioos/compliance-checker