Change background color

Really nice package!

Please add a face for changing the background color.

I now have this (works fine by the way):

```elisp
(define-key user-map (kbd "S") (lambda ()
(interactive)
(if (package-installed-p 'snow)
(progn
(snow)
(switch-to-buffer "\*snow\*") ; strange, but necessary
(scroll-up-command 5)
(face-remap-add-relative 'default :background "#2b3c44"))
(message "Error enabling Snow:\n(Searching for program No such file or directory now)"))))
```