Unify missing app error messages
Add proper error handling to each config command
Simplify env var checking in config plugin

All checks are now done within the commands, and we only need to ensure the config file exists.
Simplify if statement
Correct plugin example

$APP is not available until after the if guards
Unify the way in which all error messages are specified

Other parts of dokku use one-liners where possible, so these parts should as well
Exit 0 if there is no configuration

heroku config:get exits 0 in this case
Merge pull request #782 from progrium/simplified-config

Simplified config
Release 0.3.6
fix app plugin that was always searching for empty app name
fix search for apps if DOKKU_ROOT is a symlink
Merge pull request #788 from mmerickel/fix.apps-plugin

fix apps plugin issues in 0.3.6
do not output message when creating ENV file

This fixes a bug introduced when deploying apps where the
nginx-vhosts plugin runs ``dokku config:get $APP NO_VHOST``. The initial
run of this actually was creating the ``ENV`` file and dumping to
stdout the value "NO_VHOST=-----> Creating /home/dokku/foo/ENV". This
was obviously no good because nginx-vhosts was considering this to be a
value of true.

I've modified this to simply not return anything when the value does not
exist. A better update may be to output the messages to stderr instead
of stdout.
Merge pull request #789 from mmerickel/fix.deploy-vhost
Release 0.3.7
Merge pull request #5 from progrium/master

0.3.7