[Tagging] New proposal: Obligatory tagging of oneway on motorway_link

[Joachim]

Considering that most replies where not in favour of dropping routing
over "undefined oneway" I changed the sentence about routers:
"- For routing purposes no recommendation for ways with undefined
oneway is made. A provider should decide on it's own considering the
documentation history and current data."

The main part of the proposal is about the requirement of explicit
tagging, so I'm going with the consensus about routing. If you have
better wording, feel free to change the sentence.

Regards, Joachim