Mutable values, better iteration over lists (update 1)

 - essential to have mutable values stored in notes
 - lst.iternodes([to]) - iterator over the nodes, not just values as lst.__iter__
 - lst.nodeat(5).iternext([to]) - iterate starting the 5th node to the tail of the list
 - lst.nodeat(5).iterprev([to]) - iterate starting the 5th node to the head of the list
If argument [to] is specified, iteration stops when the current node is equal to it. Or goes to the head/tail of the list if [to] is stored in other section of the list.