includes/std: Fixed std::string::replace (#163)

The submitted fix may have been a work in progress version instead of the tested solution I intended to submit. Hopefully this time I'll get it right.

includes/std/string.pat

@@ -230,7 +230,7 @@ namespace std::string {
 				i = i + 1;
 			}
 		}
-		result = result + std::string::substr(string,string_len-pattern_len-1,pattern_len);
+		result = result + std::string::substr(string,string_len-pattern_len+1,pattern_len);
 
 		return result;
 	};