Resolve discrepancy between API and actual behavior for n-best lists

[tuetschek]

The API description puts the elements of the n-best list inside translated, but the implementation puts them inside translation. translated then contains the individual sentences of a single n-best list member.

We should unify the behavior of the code with the API description or the other way round, whichever is more reasonable.

[tuetschek]

The API description was basically right. Minor problems in the API descriptions were fixed in f59272e, 1b1aa2c, 6cbc52e, and 4636ba8. Code was fixed in 1f545ca.