Add the ability to specify "load_module" and "use" search paths. The capability is primitive and it is currently used by chaiscript_eval to set a single path from environment variables

include/chaiscript/language/chaiscript_common.hpp

@@ -113,6 +113,18 @@ namespace chaiscript
         virtual ~Eval_Error() throw() {}
     };
 
+    /**
+     * Errors generated when loading a file
+     */
+    struct File_Not_Found_Error : public std::runtime_error {
+        File_Not_Found_Error(const std::string &filename)
+           : std::runtime_error("File Not Found: " + filename)
+        { }
+
+        virtual ~File_Not_Found_Error() throw() {}
+    };
+
+
     /**
      * Special type for returned values
      */