Pyale

- allow option not to fill in empty cells in the 2D effect plot (PR 24)
- change the the way the jitter effect is computed for the rug in the 1D continoues plot (issue 6)
- fix bug in 1D continuous quantiles definition (issue 15)
- address pandas future warnings
- fix 2D plot when the two features are in two very different scales (PR 23)

The following was addressed in this release
* sklearn is deprecated (replace by scikit-learn)
* FutureWarning: Using the level keyword in DataFrame and Series aggregations is deprecated and will be removed in a future version.
* DeprecationWarning: In a future version, `df.iloc[:, i] = newvals` will attempt to set the values inplace instead of always setting a new array.

Address issues 2 and 3 :
* Allow using float discrete features
* Allow using models which return an array of singletons when predicting
* Allow using dataframes which have a special index in 2D continuous

The package with this release support categorical features, regardless of the used encoding in the model