Minimum redundancy maximum relevance (mRMR) feature selection

Hi!

I have created a new class computing the mRMR filtering feature selection.

pep8, pyflakes and nosetests run succesfully on the submitted code.

I am planning to create the documentation for this class as soon as I receive your approval.

It is my first time contributing to an open source project, so let me know if there is anything to change.

Thanks!

Andrea