Removes _DEBUG directives from all source files

This commit removes the #ifdef _DEBUG statements at the top of all source code files per issue #482. It also updates the doc files to stress that the speedup observed for hydraulic analysis with the MMD node re-ordering method only applies to single period runs.

src/qualroute.c

@@ -7,19 +7,12 @@ Description:  computes water quality transport over a single time step
 Authors:      see AUTHORS
 Copyright:    see AUTHORS
 License:      see LICENSE
-Last Updated: 11/27/2018
+Last Updated: 05/15/2019
 ******************************************************************************
 */
 
-#ifdef _DEBUG
-  #define _CRTDBG_MAP_ALLOC
-  #include <stdlib.h>
-  #include <crtdbg.h>
-#else
-  #include <stdlib.h>
-#endif
+#include <stdlib.h>
 #include <stdio.h>
-
 #include <math.h>
 
 #include "mempool.h"