Added the requirement of package Eigen3 for the linear algebra computations.
Checked and fixed the methods to compute correlation and variance-covariance structure inside dataSet class. Changed the inner representation of dataset to an Eigen matrix.
Moved the computation of var-cov matrix and cor matrix to the external VarCovStructure class, that will be expanded to allow also the
spectral decomposition of var-cov matrix and (eventually) a PCA analysis.
Completed and fixed the VarCovStructure class. Added a test inside dataSet test directory.
Added the first matrix distance: Frobenius. Added also a test directory matrixDistances. Compilation, execution and meaning checked.
Added and checked all the remaining matrix distances.
Finished to implement the permutation test.

A checkup of the use of shared_ptr to avoid side-effect modifications of class members is required.
Modified the permutation test allowing to use datasets with different cardinalities.
modification to generator of dataset in permutationTest
New modification to the permutationTest class, now there is the possibility to specify a subset of the dataset determined with a random sampling.