The Iter implementation is wrong.

[lightsing]

as long as the SIZE bit is set (which is out of bound), it will appears in iter result.

related to: #22 #18

    #[test]
    fn test_invert_iter() {
        let bitmap = Bitmap::<7>::from_value(0b11111010);
        assert_eq!(bitmap.into_iter().collect::<Vec<_>>(), vec![1, 3, 4, 5, 6]);
    }