Get mutlifile compilation working again and add a test for it

unittests/multifile_test_module.hpp

@@ -0,0 +1,11 @@
+#include <chaiscript/chaiscript.hpp>
+
+class Multi_Test_Module
+{
+  public:
+    static int get_module_value();
+
+    Multi_Test_Module();
+
+    chaiscript::ModulePtr get_module();
+};