Assorted documentation fixes

[mahrud]

• fixed typo in Polyhedra documentation
• fixed documentation of intersect and tensor
• limited protected objects listed by help
• removed extra space before colon in help
• fixed various typos
• always run codespell
• moved documentation contributors for DGAlgebras to appropriate place

[DanGrayson]

Can you fix the failing test build?

[mahrud]

Annoyingly, the words in the codespell ignore file must be lower case. It is strange to me that some of the "typos" are just variables or function names people have chosen, like allReady or tRing or aNumber.