skewt subroutines updated to handle non-celcius

[jibbals]

Description Of Changes

Updated the moist adiabats, dry adiabats, and the mixing line subroutines
to use the xaxis units. These routines originally used degrees celcius
even if the xaxis was not degrees celcius. This caused lines to be
plotted wrongly on any other units.

Checklist

Closes #1155
I don't know how to add tests

• Tests added
• Fully documented

[CLAassistant]

Thank you for your submission, we really appreciate it. Like many open source projects, we ask that you all sign our Contributor License Agreement before we can accept your contribution.
1 out of 2 committers have signed the CLA.

✅ jibbals
❌ Jesse Greenslade

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[jibbals]

I will close the pull request, and try again when I have time to figure out the process.

[zbruick]

Let us know if you have any questions about the process! The original code in this PR looked good I think. It just looks like you had commits from two different user accounts, which the CLA was complaining about then.

The tests are a little trickier for this PR, since they'll be image tests. You can find information on our page here. However, we can also help write the tests and push to your future PR, if you allow write access from maintainers when you open the PR.