Add function to compute SHAP values.

[aloctavodia]

We may use the shap package and provide a utility function to make things much simpler for users. See #147 for a discussion.

Alternatively, we may be able to take advantage of the tree representation and obtain a faster method as we did for partial dependence plots. See https://hughchen.github.io/its_blog/index.html for example

[jlevy44]

We have a function to do this and will release soon!

[aloctavodia]

hi @jlevy44, will that function be available to use from PyMC-BART?

[jlevy44]

We are not working on a PR at this time, will be part of separate repo though you are welcome to refactor and PR.

[aloctavodia]

Cool, thanks