Feature - Browser Configuration

So I've ended up doing a couple of things here:

* Added support for a g:voogle_browser configuration parameter. Not sure if there should be a more explicit message if the configuration parameter isn't valid (ie is not executable)

* Silenced the output of the external command

* Added an explicit redraw after the exec. I was having an issue with the lazyredraw, this seems to fix it.

If you have any comments/feedback, send'em my way. This was the first time I've actually looked closely at a vim plugin, so please be gentle. :)