read config also from environment variables, merge on top of json file config

lib/config.js

@@ -4,4 +4,18 @@ var _ = require('lodash');
 var config = require('../config.json');
 var env = process.env.NODE_ENV || 'development';
 
-module.exports = _.merge({}, config.all, config[env]);
+// TWITTER_CONSUMER_KEY => twitter.consumerKey
+function toPath(key) {
+  var parts = key.split('_');
+
+  var namespace = parts[0].toLowerCase();
+  var option = _.camelCase(_.tail(parts).join('_'))
+
+  return option ? [namespace, option].join('.') : namespace;
+}
+
+var envVars = _.reduce(process.env, function(memo, value, key) {
+  return _.set(memo, toPath(key), value);
+}, {});
+
+module.exports = _.merge({}, config.all, config[env], envVars);