Interface Changes

- June 12, 2009: vector0 is now vector0<> as per Boost Trac Ticket #1608
  to follow MPL more closely.
- September 24, 2009: added nview and friends
- October 12, 2009: the accumulator is the first argument to the functor of
  fold and accumulate. Fixes Boost Trac Ticket #2355.
- October 30, 2009: Added support for associative iterators & views.
  Renamed associative_sequence_tag to associative_tag. Fixes Boost Trac
  Ticket #3473.
