Add struct tests.

tests/struct.er

@@ -3,4 +3,12 @@ struct a {
     int y
 };
 
-int main() { return (0); }
+int printf(char* fmt);
+
+struct a str;
+
+int main() { 
+	str.y = 55;
+    printf("%d\n", str.y);
+	return (0); 
+}