LDA.cpp eigennized

I have changed the LAPACK codes into EIGEN3 for the binary classification through LDA.
I think you should distinguish two cases here (like in CPCA). If N are the number of points and D are the number of data then
SVD will be more efficient when D>>N
and the previous version will be more efficient for N>>D

There should be an enum to force a particular version, and there should be an automatic option.
That is just some logic to add now (there should be unit tests for both cases)

You can really follow the PCA imeplementation and unittest logic here. @parijat might also have comments.

Thanks for your great work here!