Inter-sentence coreference resolution

[RazinShaikh]

Implement different forms of coreference resolution including neural coref, proper noun matching, etc.

[BenjaminRodatz]

The code already exists. It just hasn't been integrated. In part because all tested coref resolution softwares are unsatisfactory

[JosephNathaniel]

We have integrated the inter-sentence coreference in commit 247c99b but this is done in a hacky way. For now, we simply convert the coreferences to the same word and then the name-matching composition takes care of it. We should factor it such that we can specify which kind of coreference to use and it shouldn't always reduce to name matching.