modernize ordering list docs

[Mike Bayer]

Docs repeat themselves a lot, important notes are buried in the init method. chop down the verbiage and make sure the "order by on relationship" note is prominent with a green box in the introduction.

[Mike Bayer]

didn't quite take that route but things are straightforward now.

55f24aaf6e6eb3797eb0673302c15f0b9043bcfa

11efa216e5ff17fc48b22d27e21194ed7ff8edb1

[Mike Bayer]

Removing milestone: 0.7.10 (automated comment)