Adds ability to insert env vars into config files.

Adds ability to configure apps via env vars to brunch.

Add "config-env-brunch": "x.y.z" to package.json of your brunch app.

Pick a plugin version that corresponds to your minor (y) brunch version.

If you want to use git version of plugin, add "config-env-brunch": "git+ssh://".

The plugin will process your app/ Include env vars like this:

shell = "<%= process.env.SHELL %>"