add the possibility to extend Matrix outside Eigen, just like MatrixBase
add the possibility to extend Matrix outside Eigen, just like MatrixBase

ROCmSoftwarePlatform/hipeigen,pthulhu/eigen,ritsu1228/eigen,cjntaylor/eigen,TSC21/Eigen,cjntaylor/eigen,Zefz/eigen,TSC21/Eigen,pthulhu/eigen,pasuka/eigen,toastedcrumpets/eigen,pthulhu/eigen,ritsu1228/eigen,Zefz/eigen,toastedcrumpets/eigen,toastedcrumpets/eigen,TSC21/Eigen,cjntaylor/eigen,ritsu1228/eigen,Zefz/eigen,cjntaylor/eigen,pasuka/eigen,pthulhu/eigen,ritsu1228/eigen,toastedcrumpets/eigen,ritsu1228/eigen,pasuka/eigen,ROCmSoftwarePlatform/hipeigen,pasuka/eigen,ROCmSoftwarePlatform/hipeigen,ROCmSoftwarePlatform/hipeigen,pasuka/eigen,Zefz/eigen,pthulhu/eigen,TSC21/Eigen