add eigen

swift/core/Eigen/Cholesky

swift/core/Eigen/CholmodSupport

swift/core/Eigen/Core

swift/core/Eigen/Dense

swift/core/Eigen/Eigen

swift/core/Eigen/Eigenvalues

swift/core/Eigen/Geometry

swift/core/Eigen/Householder

swift/core/Eigen/IterativeLinearSolvers

swift/core/Eigen/Jacobi

swift/core/Eigen/KLUSupport

swift/core/Eigen/LU

swift/core/Eigen/MetisSupport

swift/core/Eigen/OrderingMethods

swift/core/Eigen/PaStiXSupport

swift/core/Eigen/PardisoSupport

swift/core/Eigen/QR

swift/core/Eigen/QtAlignedMalloc

swift/core/Eigen/SPQRSupport

swift/core/Eigen/SVD