[feature request] Add more detailed outputs to score_batch()

[vince62s]

Hello,

I know this is for a specific use-case but today the score_batch() function returns only the argmax() which enables only to score and get the logprob/perplexity of a sentence, file, ...

In a scenario where we need all scores for each word in the vocab to be able to use against an MT ouput, one could need the full detailed output, in the same format as the onmt-py generator.

whenever, if possible.

Thanks, Vincent