add demo volume code

demo/volume/include/space.h

@@ -0,0 +1,13 @@
+/*
+ * ALGO     : PROJ. : Volume
+ * RESEARCH : File  : space.h
+ *          : Date  : 20100531.0725UTC
+ *          : Email : mail@algoresearch.net
+ */
+
+#include <stdlib.h>
+#include <unistd.h>
+
+void create_space(SYS_TABLE *sys, int w, int h, int d);
+void iterative_space (SYS_TABLE *sys);
+int cell_get(SYS_TABLE *sys, int x, int y, int z);