Bnlearn

* Functionally added to make predictions on dataset with the *predict* function 17
* Predict examples can be found in the readme and sphinx pages: https://erdogant.github.io/bnlearn/pages/html/Predict.html
* Functionally added that outputs a dataframe with the results for the inference that is made (*query2df*)
* Included some exceptions to catch errors
* Fixed circular imports
* Unit test updated for the new functions
* Some docstrings updated
* Some code refactoring and cleaning

* New functionality added: topological sorting of the DAG.
* Example of usage: https://erdogant.github.io/bnlearn/pages/html/topological_sort.html

* Fix for the maximum likelihood estimation in parameter learning using the model.fit approach (thanks to ssomanch)

* Fix typo in pip install instructions
Thanks to the contribution of bencevans!

* tabu_length is configurable in hill climb search (Thanks to contribution of ivylee!)

* the use of black_list and white_list requires setting parameter method type
* update unit test
* update sphinx docs