rename DEBUG define to TINYXML2_DEBUG

The original name is to general. This prevents possible name collisions with other defines, enums, etc. from projects where tinyxml2 is used.
diff --git a/tinyxml2.h b/tinyxml2.h
index 4cc694b..85cb497 100755
--- a/tinyxml2.h
+++ b/tinyxml2.h
@@ -47,15 +47,15 @@
 */

 /*

 	gcc:

-        g++ -Wall -DDEBUG tinyxml2.cpp xmltest.cpp -o gccxmltest.exe

+        g++ -Wall -DTINYXML2_DEBUG tinyxml2.cpp xmltest.cpp -o gccxmltest.exe

 

     Formatting, Artistic Style:

         AStyle.exe --style=1tbs --indent-switches --break-closing-brackets --indent-preprocessor tinyxml2.cpp tinyxml2.h

 */

 

 #if defined( _DEBUG ) || defined (__DEBUG__)

-#   ifndef DEBUG

-#       define DEBUG

+#   ifndef TINYXML2_DEBUG

+#       define TINYXML2_DEBUG

 #   endif

 #endif

 

@@ -79,7 +79,7 @@
 #endif

 

 

-#if defined(DEBUG)

+#if defined(TINYXML2_DEBUG)

 #   if defined(_MSC_VER)

 #       // "(void)0," is for suppressing C4127 warning in "assert(false)", "assert(true)" and the like

 #       define TIXMLASSERT( x )           if ( !((void)0,(x))) { __debugbreak(); }

@@ -395,7 +395,7 @@
         }

         --_currentAllocs;

         Item* item = static_cast<Item*>( mem );

-#ifdef DEBUG

+#ifdef TINYXML2_DEBUG

         memset( item, 0xfe, sizeof( *item ) );

 #endif

         item->next = _root;