Ability to resize based on width or height, and adjust the other value accordingly

```
The plugin seems to require both width and height values to be entered, which 
rules out the ability to scale an image according to either its width/height 
proportionately.

Is there a way to achieve this please? 


```

Original issue reported on code.google.com by `lin.fred...@gmail.com` on 17 Jun 2011 at 7:32
