kdtree 0.5.7

Changes:

• added support for standard config.h [J.J. Green]
• improved the makefile including soname and ldname links, DESTDIR, and creating missing directories on install
• fixed example program build [Jett]
• fixed kd_res_item3 and kd_res_item3f not returning the data pointer
• fixed kd_res_item3 and kd_res_item3f not checking if the position pointers are null [Mo DeJong]