added function to add 2D latlon to dataset

[snowman2]

• Tests added
• Fully documented, including whats-new.rst for all changes and api.rst for new API

[djhoese]

Does this still work if someone has a +proj=latlong projection and 1D longitude and latitude coordinates that they use as their X and Y coordinates?

[snowman2]

Does this still work if someone has a +proj=latlong projection and 1D longitude and latitude coordinates that they use as their X and Y coordinates?

It should. As long as they don't have 'latitude' and 'longitude' in the coordinates it will generate a 2D array of latitude and longitude.