Shap

This release includes:
- Support for sklearn isolation forest courtesy of JiechengZhao
- New check_additivity tests to ensure no errors in DeepExplainer and TreeExplainer
- Fix 861, 860
- Fix missing readme example html file
- Support for spark decision tree regressor courtesy of QuentinAmbard
- Better safe isinstance checking courtesy of parsatorb
- Fix eager execution in TF < 2 courtesy of bottydim

This release contains several new features and bug fixes:
- GradientExplainer now supports TensorFlow 2.0.
- We now do a lazy load of the plotting dependencies, which means a pip install no longer needs to also pull in matplotlib, skimage, and ipython. This should make installs much lighter, especially those that don't need plotting :)
- Added a new BruteForceExplainer for easy testing and comparison on small problems.
- Added a new partial_dependence_plot function. This function will be used to illustrate the close connections between partial dependence plots and SHAP values in future example notebooks.
- Handle the multiclass case with no intercept in LinearExplainer courtesy of gabrieltseng
- Some extras_require options during the pip install courtesy of AbdealiJK
- Other small bug fixes and updates

This release is primarily to remove a dependency on dill that was not in setup.py. It also includes:

- A typo fix in force.py courtesy of jonlwowski012
- Test code cleanup courtesy of jorgecarleitao

- Fix floating point rounding mismatches in recent sklearn versions of tree models
- An update to allow easier loading of custom tree ensemble models by TreeExplainer.
- `decision_plot` documentation updates courtesy of floidgilbert

- New decision_plot function courtesy of floidgilbert
- Add alpha version of the new model agnostic PartitionExplainer
- ensure data is all on the same device for pytorch in DeepExplainer courtesy of gabrieltseng
- fix lightgbm edge case issue courtesy of imatiach-msft
- create binder setup for shap courtesy of jamesmyatt
- Allow for multiple inputs in the gradient explainer courtesy of gabrieltseng
- New KernelExplainer unit tests courtesy of jorgecarleitao
- Add python 2/3 trove classifiers courtesy of proinsias
- support for pyspark trees courtesy of QuentinAmbard
- many other bug fixes courtesy of Rygu, Kylecrif, trams, imatiach-msft, yunchuankong, invokermain, lupusomniator, satyarta, jotsif, parkerzf, jaller94, gabrieltseng, and others

- Fixes an issue in DeepExplainer caused by a change in TensorFlow 1.14.