clear_pattern method broken in release

In the 0.3.1 release version, the `clear_pattern` call fails with `NameError: name 'write_pattern_line' is not defined` on this line:

```
          rc = write_pattern_line(self.dev, 0, 'black', i );
```

This is actually fixed in the code in the repo, so I think all this needs is releasing a new version, and possibly adding a test for the clear_pattern method.