spatial-trees: A C repository from mtiberti

Original code by Steven Skiena and Michael Murphy, explicitly put in "public domain" 
at request on 10-28-2011
Modified for encapsulation into a library by Scott Locklin

zlib license

Ranger was a cool-looking demonstration of how spatial trees work, and how they break
down in higher dimensions; aka, everything in high dimensions is pretty close to everything
else. I've looted the code, because there aren't enough spatial trees around which are
written in good old C. If I can get these things to work properly, I'll build hooks in 
J and Lush (and possibly R, if there are any advantages of, say, VPtrees over libANN).

libANN and libFLANN are good libraries for this sort of thing, but they are also large and
complex, making them difficult to modify. These trees are simple enough to understand in
an afternoon, and easier to fiddle with. I also prefer the simplicity of C.

If I can get them working properly, I plan to modify them heavily for readability and 
performance.

Presently optkd is tested. It's weird, and contains icky globals, but it works
Sproull is tested and doesn't work. Same with VP and naivekd. 
VP has a memory issue, and naivekd has a weird query syntax that makes no sense to me.

Naive works ;-)

Original Ranger code can be found here:
http://www.cs.sunysb.edu/~algorith/implement/ranger/distrib/

With documentation from the famous book here:
http://www.cs.sunysb.edu/~algorith/
mtiberti/spatial-trees
