Binded SVD in the python level and documented

Implemented the signal standarization. The signs of U and V is defined analysing the first element of U.
If U[0, 0] < 0 then U=-1*U and V=-1*V
With that we have a consistent SVD binds along different implementations (http://prod.sandia.gov/techlib/access-control.cgi/2007/076422.pdf)