Bayesml

* Fixed a bug in ``visualize_model()`` of the bernoulli model and the categorical model.
* Update the Web pages

* Accelerate the posterior updating algorithm in [meta-tree model](https://yuta-nakahara.github.io/BayesML/bayesml.metatree.html "BayesML Meta-tree Model")
* Improve stability of [gaussian mixture model](https://yuta-nakahara.github.io/BayesML/bayesml.gaussianmixture.html "BayesML Gaussian mixture Model") and [hidden Markov normal model](https://yuta-nakahara.github.io/BayesML/bayesml.gaussianmixture.html "BayesML Hidden Markov normal Model")

* Bug fix in [meta-tree model](https://yuta-nakahara.github.io/BayesML/bayesml.metatree.html "BayesML Meta-tree Model")

* Modified tree visualization in [meta-tree model](https://yuta-nakahara.github.io/BayesML/bayesml.metatree.html "BayesML Meta-tree Model") and [context tree model](https://yuta-nakahara.github.io/BayesML/bayesml.contexttree.html "BayesML Context Tree Model").

* [Meta-tree model](https://yuta-nakahara.github.io/BayesML/bayesml.metatree.html "BayesML Meta-tree Model") supported continuous explanatory variables.
* Minor change of [context tree model](https://yuta-nakahara.github.io/BayesML/bayesml.contexttree.html "BayesML Context Tree Model").
* Model constants are clarified with `c_` prefix.

The following models and their documents are newly added.

* [Gaussian mixture model](https://yuta-nakahara.github.io/BayesML/bayesml.gaussianmixture.html "BayesML Gaussian Mixture Model")
* [Meta-tree model](https://yuta-nakahara.github.io/BayesML/bayesml.metatree.html "BayesML Meta-tree Model")
* [Hidden Markov normal model](https://yuta-nakahara.github.io/BayesML/bayesml.hiddenmarkovnormal.html "BayesML Hidden Markov Normal Model")
* [Context tree model](https://yuta-nakahara.github.io/BayesML/bayesml.contexttree.html "BayesML Context Tree Model")