Add documentation comments to opmodes and features

[MatthewL246]

I will add documentation comments to the opmodes and features.

I think each opmode comment should have a short description and links to the features used, and each feature comment should have a short description, requirements for attached devices, and controls.

[MatthewL246]

Replacement for #549 because I renamed my branch to follow the new feature branch style.

[MatthewL246]

Feel free to add more documentation for the things I skipped because I didn't understand them.

Also, I personally like this documentation format but feedback is welcome.