fix compiling issue for windows

Author: francoisbonneau

include/geode/stochastic/spatial/details/RTree.hpp

@@ -8,6 +8,7 @@
 // NOTE These next few lines may be win32 specific, you may need to modify them
 // to compile on other platform
 #include <assert.h>
+#define _USE_MATH_DEFINES
 #include <math.h>
 #include <stdio.h>
 #include <stdlib.h>