Dython

* Added `data_utils.one_hot_encode`
* Added `title` and `filename` options to `associations` and `roc_graph`

* Added configurable `vmax` and `vmin` to `nominal.associations` (issue [68](https://github.com/shakedzy/dython/issues/68))

* Bug fix in `model_utils.roc_graph`
* `model_utils.roc_graph` now accepts also `legend` and `plot` arguments

* New module: `data_utils`
* `split_hist` method added, with new example
* `identify_columns_by_type` and `identify_columns_with_na` moved to `data_utils` from `nominal`

* Added `nominal.identify_columns_with_na` (by **[musketeer191](https://github.com/musketeer191)**)
* Added `nominal.identify_numeric_columns` (issue [58](https://github.com/shakedzy/dython/issues/58), by **[musketeer191](https://github.com/musketeer191)**)
* Added `nominal.identify_columns_by_type`
* `nominal.identify_nominal_columns` no longer accepts the `include` parameter (use `nominal.identify_columns_by_type` instead)
* Fix docstring of `nominal.compute_associations` (issue [55](https://github.com/shakedzy/dython/issues/55))
* Requires Pandas 0.23.4 or greater (was required before, but not specified in setup file)

* Resolve issues [48](https://github.com/shakedzy/dython/issues/48) and [#49](https://github.com/shakedzy/dython/issues/49)