Coordinating docs with new logging

[john-science]

I found two errors while trying to build the docs today:

1. The new Sphinx 4.x version of has a bug that affects us: more than one target found for cross reference should prefer current file's method over other libraries methods sphinx-doc/sphinx#4961
2. Because of how logging works, it will sometimes run in a realm free of our changes to logging, but sometimes will import ARMI code and very much be in our logging world.

So, the fixes to these are easy:

1. @ntouran showed he was able to eliminate the Sphinx bug by running in v3.5. But this didn't work for me. So I have set the requirement to exactly the version that worked for me.
2. In two places in the /docs/ folder, I manually set/reset the logging to be the Python standard library version, or ours, when we need.

So the errors are fixed and the docs build, hurray! But there are still many warnings being thrown while building the docs that will have to be addressed.