Added DivisionOperatorFix option for signed integer division (#278)

* it changes the behavior of vanilla division operator to use signed
integer division. Before it used signed division for floats but
unsigned for integers.

Added a new "div" operator for unsigned integer division.
Moved mathematical script functions from Utils.cpp to new Math.cpp.
Added include guard to sfall.h and main.h in modders pack.

artifacts/mods/main.h

@@ -1,3 +1,5 @@
+#ifndef MAIN_H
+#define MAIN_H
 
 #include "..\scripting\headers\sfall.h"
 #include "..\scripting\headers\define_lite.h"
@@ -71,3 +73,5 @@ end
 procedure InitConfigs begin
    translationIni := GetIniConfigStr("Main", "TranslationsINI", "Translations.ini", "ddraw.ini");
 end
+
+#endif