updated autoencoder/topicmodeling


Former-commit-id: b36b54e6b55d6900ab52047ec2ace7a27243f3e4
initial backprop; does not work, merely a prototype


Former-commit-id: 538c51d8d63a92a572800ff0eb39c9cb44f49644
cleanup


Former-commit-id: a5ecde5552da3148afb039e44b8740e8f0589492