Implement DAAT scoring

[elshize]

When scoring on-the-fly, it might matter how many look-ups to the size table is made, so implementing a DAAT-specific scoring---which scores entire document at once---might be a good idea.

However, I have doubts it matters much, as the intersection might not be big enough to make a difference.

Another reason for this could be finding out how precision changes if we score with a smoothed language model, and always consider all terms, even those for which a document doesn't exist in the posting list.