clean up config/database.yml.

Hey folks, note that usernames, passwords, and other secrets should never be checked into version control. Normally you .gitignore this file, but in this case we don't need to because:

1) postgres will attempt to connect using your current username if none is provided, so we can leave username blank and password blank, and it should work on all dev machines. neat!

2) heroku doesn't use this file, so we don't need to specify the production password, or even the production environment at all!

So here is your clean new config/database.yml, safe to keep in version control.

P.S. don't worry about what &TEST means for now, but you don't need it. :)