Add warning for radians flag with Proj class

[snowman2]

• Start of ENH: Add support for radians for Proj & Transformer.from_pipeline #612
• Tests added
• Fully documented, including history.rst for all changes and api/*.rst for new API

[snowman2]

@djhoese, just a ping to let you know about this change - it means you shouldn't need to worry about the previous ping in the release issue.

[djhoese]

Thanks! As you know, pyresample plans on transitioning to using new pyproj features "soon". The only reason this custom class exists that was passing the old radians kwarg was to get degrees when given degrees for a latlong projection. Thanks for making this a warning instead for now.

Just curious, the support for radians in pyproj 3, does that change the degrees -> degrees default for lat/lon projections?

[snowman2]

The default of degrees will remain in pyproj 3. The only change will be that you can use radians if you want.