Analytic Saturation Vapor Pressure

[dcamron]

Dependent on #3725.

In a Christmas Eve sprint, I implemented the analytic saturation vapor pressure from Ambaum 2020, per recommendations from #626. Lots of updated test values, and these may change further, but I wanted to get the changes out there quickly so we could evaluate their impacts, as well as get the changes into the full test matrix.

All departures are small in relative magnitude, but some callouts for potential scrutiny:

• test_sensitive_sounding
• test_lfc_ml
• test_el and its extensions
• any test involving cape_cin (mentioned in issue above as impacted, and needs LCL changes to see full picture.)
• test_dewpoint_specific_humidity_xarray (I reduced the precision instead of redefining the test data)

test_equivalent_potential_temperature_masked worked before. The calculations work on the individual masked array elements but for some reason it blows up on the full array. numpy.ma.exp offered no help. If anyone has any insight here it had me pulling my hair out a bit.

I'm not touching image tests until the other PR goes in and we tackle a review here, and maybe not even until LCL.

I'll include an implementation and tests for the saturation vapor pressure over ice in this PR as well.

Happy holidays! 🎅

• Tests added
• Fully documented

[dopplershift]

I think it makes sense to do this by itself. I don't understand why the test is failing with overflow in exp(). I can get the test suite to fail, but I can't get it to warn when running in a notebook.