Added prototype Response System library port from the Alien Swarm SDK

sp/src/responserules/runtime/rrrlib.cpp

@@ -0,0 +1,13 @@
+/// PLACEHOLDER FILE FOR RESPONSE RULES RUNTIME LIBRARY 
+
+#include "rrbase.h"
+
+// memdbgon must be the last include file in a .cpp file!!!
+#include "tier0/memdbgon.h"
+
+
+namespace ResponseRules 
+{
+	/// Custom symbol table for the response rules.
+	CUtlSymbolTable g_RS;
+};