Make core/ includes absolute, remove subfolders from include path

This allows more consistency in the manner we include core headers,
where previously there would be a mix of absolute, relative and
include path-dependent includes.

core/math/quick_hull.cpp

@@ -29,7 +29,8 @@
 /*************************************************************************/
 
 #include "quick_hull.h"
-#include "map.h"
+
+#include "core/map.h"
 
 uint32_t QuickHull::debug_stop_after = 0xFFFFFFFF;