Add MI estimators in R

[pawel-czyz]

As @a-marx told me, KSG, G-KSG, gKNN, and LNN are implemented in this repository. For the demo, look here, at lines 97–113.

We can add it as a git submodule and plug it into our framework by creating an appropriate wrapper script in R. It it probably the best to parametrize it with argparse.

[a-marx]

LNN is implemented in the rmi R package.

[pawel-czyz]

We added the estimators from the rmi library.