Improvement: A user can now use a flag to specify which mode to use when parsing `app.conf`.

Hi Herman,

Thank you for the great post and good repo.

Inspired by your post, I managed to write my first lines of Go and even have a running instance of it at heroku.

Getting it all working was not too hard, except for the part where I needed to add the admin user, which was easy on my dev machine, but a bit harder on heroku. So I wrote this little patch that lets you specify which `mode` to use from `app.conf` when running the ironzebra command.

Usage:
    
    $ heroku run ironzebra --mode=prod github.com/<your_name>/ironzebra adduser

Hope you like it,

Marko