Several users have requested LDA using asymmetric priors, including learning those hyperparameters. We should add this functionality.
Note that it could be added to EM, online LDA, or both. I suggest adding it to online LDA initially, followed by EM in a separate PR.
This JIRA is now limited to the document-topic prior (docConcentration). See linked JIRA for topicConcentration, which is lower priority.