master-84634c0

Elide logits if the logits pointer parameter is NULL (#107)

* Completely skip calculation of logits if nobody cares

This speeds up sequence mode evaluations by up to 20% if you ingest
a large prompt and then only retrieve the logits at the very end.

Note that you must pass a NULL pointer to the logits parameter in
order to take advantage of this optimization.

* logits_out=NULL documentation