Document most everything.

Some things are left undocumented, where they are uninteresting or REALLY
self-apparent. Adds `#[deny(missing_doc)]` to `render` and `device`, but also
some well-placed `#[allow(missing_doc)]`.

Closes #114
I like to think of them like that... "Attribute" is not a very helpful explanation of what it does. I struggle to find a better description, do you have one?