Configurable width

[mortenlj]

I've just discovered this extension, and it's great! One thing that would make it better, is to be able to configure how much of the screen to use. Most of the time I think the default width github uses is too narrow, but often I'm on a huge screen and using the full width of the window is a bit too much. Would be great to set a percentage of the width to use.

[caruccio]

Wish I could send you a +1000