Dtreeviz

See https://github.com/parrt/dtreeviz/milestone/40?closed=1

Contributors
* 2 items: [Tudor Lapusan](https://github.com/tlapusan) (tlapusan)
* 1 items: [StepanWorkV](https://github.com/StepanWorkV) (StepanWorkV)
* 1 items: [Tyrion](https://github.com/hxhxd) (hxhxd)

Issues fixed
* [TypeError: dict() argument after ** must be a mapping, not float](https://github.com/parrt/dtreeviz/issues/285) (compatibility)
* [Visualisation error when a node will contains samples from only one class (sklearn)](https://github.com/parrt/dtreeviz/issues/283) (bug)
* [Pie charts show for data that classifier was trained on and not new data](https://github.com/parrt/dtreeviz/issues/269) (enhancement)

Improvements, features
* [Make sklearn visualisations to support validation datasets.](https://github.com/parrt/dtreeviz/pull/282) (enhancement)
* [Pie charts show for data that classifier was trained on and not new data](https://github.com/parrt/dtreeviz/issues/269) (enhancement)
* [Add different display types for leaf_distributions x-axis.](https://github.com/parrt/dtreeviz/pull/254) (enhancement)

Contributors
* 4 items: [Tudor Lapusan](https://github.com/tlapusan) (tlapusan)
* 1 items: [Alex Moldovan](https://github.com/Alex-AMC) (Alex-AMC)
* 1 items: [Rajdeep](https://github.com/RajdeepTarafder) (RajdeepTarafder)
* 1 items: [HannahAlexander](https://github.com/HannahAlexander)
* 1 items: [Matthew Epland](https://github.com/mepland) (mepland)

Support string categorical vars in regressors and classifiers. See https://github.com/parrt/dtreeviz/pull/265

Minor improvement release: https://github.com/parrt/dtreeviz/pull/259

Add doc for feature space partitioning functions. Fix bug in tessellate() function.

Fix compatibility issue with tensorflow trees.