I think originally I had envisioned this as `ostree.version`, but at the last
minute we changed it to just `version`. That's what all of the code uses, so
let's fix the docs.
Closes: #638
Approved by: paulvt
Just keeping my promise to write more documentation. There could be a
lot more to write here, but I'm trying to get a start done.
Closes: #222
Approved by: jlebon