mdds 0.3.0

  * implemented point_quad_tree.

mdds 0.2.1

  * added example files on how to use these data structures.

  * fixed a bug in segment_tree::search_result object, to make it work 
    with empty result set.  

  * fixed segment_tree to make it really usable outside of unit test code.

mdds 0.2.0

  * other general performance improvements.

  * lots of code cleanups.

  * support for search result iterator in segment_tree and 
    rectangle_set, for better search performance.  

  * implemented rectnagle_set.

  * fixed lots of bugs in the segment_tree implementation.

mdds 0.1.2

  * implemented segment_tree.

  * node_base class is now without virtual methods to avoid vtable 
    generation.