Slicing w/o copying (Views)

[vkostyukov]

There are a couple of operations in matrix/vector interface that involves full copying - getRow/getColumn and slice operations sliceX. I should think of either making these operations fast of providing an alternative way doing the same task w/ coping. It usually called view. Like this:

Matrix {
  Vector getRowView();
  Vector getColumnView();
  Vector toRowVectorView();
  Vector toColumnVectorView();
  Matrix sliceView();
  Matrix sliceLeftView();
  Matrix sliceRightView();
  Matrix selectView();
}