Update minorly eigtj/svdtj related codes and doc (benchmark, matfaust,...

Update minorly eigtj/svdtj related codes and doc (benchmark, matfaust, pyfaust, pyx and C++ backend).

- The benchmark was errorneously commented and this commit changed the stopping criterion to the error instead of iteration number.
- Comment useless copy in Faust::GivensFGFTComplex.
- Handle a matrix storage order issue in _FaustCorePy.pyx eigtj wrapper.
- Update matfaust eigtj doc and add examples.
- Rename maxiter argument to nGivens.
- Update matfaust unit tests consequently.
- Update pyfaust unit tests to check the nnz number of eigenvectors transform outputs of eigtj.
- Add new examples in doc.
- maxiter > nGivens.
- Fix minor bugs in parsing of svdtj arguments.