ENH: several improvements for linked-lists

- support move construct/assignment for linked-lists themselves
  and when moving into a 'normal' list

- better consistency with begin/end signatures and the various
  iterators.

- for indirect linked-lists, provide iterator access to the underlying
  data element address:   iter.get()  vs  &(iter())

- add standard '->' indirection for iterators (as per normal STL
  definitions)