Support for gensim's AuthorTopic model

[tmthyjames]

Currently when I try to run LDAviz on gensim's AuthorTopic mode I get the following error

---------------------------------------------------------------------
TypeError                           Traceback (most recent call last)
<ipython-input-74-ac4a18d60a1e> in <module>()
----> 1 data = pyLDAvis.gensim.prepare(model, corpus, dictionary)
      2 data

/home/ubuntu/anaconda3/lib/python3.6/site-packages/pyLDAvis/gensim.py in prepare(topic_model, corpus, dictionary, doc_topic_dist, **kwargs)
    109     See `pyLDAvis.prepare` for **kwargs.
    110     """
--> 111     opts = fp.merge(_extract_data(topic_model, corpus, dictionary, doc_topic_dist), kwargs)
    112     return vis_prepare(**opts)

/home/ubuntu/anaconda3/lib/python3.6/site-packages/pyLDAvis/gensim.py in _extract_data(topic_model, corpus, dictionary, doc_topic_dists)
     40           gamma = topic_model.inference(corpus)
     41       else:
---> 42           gamma, _ = topic_model.inference(corpus)
     43       doc_topic_dists = gamma / gamma.sum(axis=1)[:, None]
     44 

TypeError: inference() missing 3 required positional arguments: 'author2doc', 'doc2author', and 'rhot'

[cpsievert]

Seems as though you should report that here -- https://github.com/bmabey/pyLDAvis