Have concatenate support lists (#233)
Have concatenate support lists (#233)

* support list in concatenate fwd

* shorter

* trying to make bwd concatenate support lists

* put conversion behind flag

* change format to multiple fwd functions

spacy-io/thinc,explosion/thinc,spacy-io/thinc,explosion/thinc,explosion/thinc,explosion/thinc,spacy-io/thinc