update the sparse tutorial wrt not so recent changes about the filling API
update the sparse tutorial wrt not so recent changes about the filling API

rotorliu/eigen,madlib/eigen_backup,mjbshaw/Eigen,rotorliu/eigen,mjbshaw/Eigen,rotorliu/eigen,rotorliu/eigen,madlib/eigen_backup,madlib/eigen_backup,mjbshaw/Eigen,mjbshaw/Eigen,madlib/eigen_backup