Document more!

[Ogeon]

There are a lot of undocumented parts, and I would love to give them some good explanations that will help newcomers as well as more advanced users. I'm not an advanced user (I just made some bindings 🙃), so i would love to get help and input from anyone who can flesh it out and fill in the blanks. You don't have to do everything if you decide to help. Any amount is most appreciated!

This attribute should also be added to lib.rs when everything is finally documented:

#![cfg_attr(feature = "strict", deny(missing_docs))]