feature request: delete progressbar when finished

```
This is a simple feature request, to delete the progressbar when finished. This 
one-line change to ProgressBar.finish seems to do the trick:

        self.fd.write('\r'+' '*self.term_width+'\r')
```

Original issue reported on code.google.com by `dsdal...@gmail.com` on 3 Nov 2014 at 4:52
