AVL library updated

[Adrian Hey]

Hello,

I've just updated the AVL library to 2.2:
 http://homepages.nildram.co.uk/~ahey/HLibs/Data.Tree.AVL/

This version has..
* A few more set manipulation functions.
* A kind of cheap but extremely limited zipper which uses
  node indexing instead of building a path structure on the
  heap.
* Some functions which may end up not modifying a tree (e.g.
  deletion of non-existing element) now return the original
  tree (rather than an identical copy with nodes on the
  search path duplicated).

Regards
--
Adrian Hey