Tomotopy

* Now `tomotopy.PAModel.infer` returns both topic distribution nd sub-topic distribution.
* New methods get_sub_topics and get_sub_topic_dist were added into `tomotopy.Document`. (for PAModel)
* New parameter `parallel` was added for `tomotopy.LDAModel.train` and `tomotopy.LDAModel.infer` method. You can select parallelism algorithm by changing this parameter.
* `tomotopy.ParallelScheme.PARTITION`, a new algorithm, was added. It works efficiently when the number of workers is large, the number of topics or the size of vocabulary is big.
* A bug where `rm_top` didn't work at `min_cf` < 2 was fixed.

* Wrong topic assignments of `tomotopy.LLDAModel` and `tomotopy.PLDAModel` were fixed.
* Readable `__repr__` of `tomotopy.Document` and `tomotopy.Dictionary` was implemented.

* A bug at init function of tomotopy.PLDAModel was fixed.

* New models including `tomotopy.PLDAModel` and `tomotopy.HLDAModel` were added into the package.

* An issue where `get_topic_dist()` returns incorrect value when `min_cf` or `rm_top` is set was fixed.
* The return value of `get_topic_dist()` of `tomotopy.MGLDAModel` document was fixed to include local topics.
* The estimation speed with `tw=ONE` was improved.

Update
* A new model, `tomotopy.LLDAModel` was added into the package.
* Since hyperparameter estimation for `HDPModel` was implemented, the result of `HDPModel` may differ from previous versions. If you want to turn off hyperparameter estimation of HDPModel, set `optim_interval` to zero.

Fixed bugs
* A crashing issue of `HDPModel` was fixed. (6)