Wet bulb potential temperature

[sec147]

Description Of Changes

Add function to calculate wet bulb potential temperature to calcs, with associated docstring and (minimal) test.
This is my first ever pull request - I've read all the docs and tested and think it's ok. Would value feedback.

Checklist

• Tests added
• Fully documented

[CLAassistant]

All committers have signed the CLA.

[dopplershift]

Thanks for the contribution! At first I was concerned this would be fundamentally different from the Bolton 1980 stuff we've used before, but I see this actually explicitly relies on it--that's great! Just a few minor tweaks to improve the docs (especially for the web) and to improve the implementation a bit. Otherwise, it looks good!

[kgoebber]

@sec147 just pinging to see if you have any cycles to address the comments on this PR and ability to rebase on main and address any conflicts that might have crept in while this was being worked on. If not, just let us know and we can move it forward from what you have submitted up to this point.

[dopplershift]

Ok, git surgery taken care of. I think this is good to go, but I added a commit renaming wetbulb to wet_bulb for consistency with the existing wet_bulb_temperature.

Need a review from @dcamron since I committed here.