release 0.8.1

[wholmgren]

We should finish up 0.8.1 before the holiday break. We're close to a good set of changes for 0.8.1, and we have a big PR (#1076) that is close to ready and will put us on the 0.9 cycle.

My suggestions for the current items open and tagged with 0.8.1 milestones:

• ENH: infinite sheds #717. Kick to 0.9.
• Improve docstring or behavior for irradiance.get_total_irradiance and irradiance.get_sky_diffuse #949. Kick to 0.9.
• Add numpy SPECTRL2 implementation #1062. @kanderso-nrel can you finish this soon?
• Refactor detect_clearsky #1074. Appears to be mostly complete but needs a full review. Might be a couple of related issues that need to be tagged too.
• add python 3.9 to ci configuration #1102. I'll work on this.

[kandersolar]

#1062. @kanderso-nrel can you finish this soon?

Yes, I will try to get that done this week. Thanks to all who reviewed!

[mikofski]

Sorry for being a stick in the mud. I'll have more time to work over the break on #717 and #949 for v0.9. thanks!

[kandersolar]

Maybe bump #1062 to 0.9.0? Checking against the reference isn't a small job and the holidays are coming up quick.

[wholmgren]

Is the comparison in the first post of #1062 not sufficient? It looked good to me. I'll review #1074 this afternoon.