Function and documentation cleanup

[martinju]

• Went through and updated the documentation for all functions, trying to make the style more consistent throughout the package with links etc. Also made sure all exported functions are documented. Reuse documentation whenever possible.
• Ensure only functions that needs to be exported actually are exported. The rest are not exported. Functions used in pyhton needs to be exported, but if they are not intended to be used by the end user, the keyword internal is used, such that they do not show up in the list of user functions.
• Remove the additional seed argument from the boostrap-functions. (Such that the seed argument passed to explain() controls the whole thing).
• Replace ::: with a surrounding \dontrun{ in examples of internal functions (CRAN will complain about :::)
• Some function/argument changes
  • default_doc_explain -> default_doc_export
  • default_doc -> default_doc_internal
  • sample_features_cpp -> sample_coalitions_cpp (+args: n_features -> n_coalitions)
  • observation_impute_cpp: arg xtrain -> x_train, xtest -> x_explain
  • compute_AICc_each_k: arg Xtest-> Xexplain
  • distance_matrix : arg Xtest_mat-> Xexplain_mat
  • setup_approach.timeseries: arg timeseries.fixed_sigma_vec-> timeseries.fixed_sigma
  • create_marginal_data_categoric -> create_marginal_data_cat
  • check_categorical_valid_MCsamp: arg joint_probability_dt -> joint_prob_dt
  • mahalanobis_distance_cpp: arg Xtest_mat -> Xexplain_mat
  • observation_impute_cpp: arg: xtrain -> x_train, xtest -> x_test
  • compute_shapley_new -> compute_shapley
• Remove MSEv from explain_forecast (as it was only supported for horizon=1). Should return in a more general manner in the future.

Other minor mentions

• Remove duplicate of function boostrap_shapley, and other unused function.
• Remove TODOs mentioned in the code

[LHBO]

Read through the changes it looks good when you make the changes we talked about on Teams.