Fixed HdpModel.print_topics and added HdpModel.show_topics

Fixes #189. HdpModel.show_topics and HdpModel.print_topics now have the same functionality as LdaModel.show_topics and LdaModel.print_topics.
Merge remote-tracking branch 'upstream/develop' into develop
HdpModel.print_topics now has an informative docstring and prints to log.

Resolves #189.
Merge pull request #190 from Tiepies/develop

Fixed HdpModel.print_topics and added HdpModel.show_topics