[mdds] R-tree documentation is now available

[Kohei Yoshida]

Hi there,

Just a short-n-quick announcement that I've finished authoring
documentation for R-tree - the newest addition in mdds.

http://kohei.us/files/mdds/doc/rtree.html

I've also updated the doc for flat_segment_tree and multi_type_vector,
to add a bit more code examples.

Best,

Kohei

-- 
Kohei Yoshida, LibreOffice Calc volunteer hacker