Adds support for local (developer) configuration

@@ -5,7 +5,7 @@ var _ = require('underscore')
 var util = require('util')
 var mergeDefaults = require('merge-defaults')
 
-exports = module.exports = function(config) {
+exports = module.exports = function(config, local) {
 
   var settings = {}
 
@@ -14,7 +14,10 @@ exports = module.exports = function(config) {
   if (!_.isObject(config[env]))
     throw new Error(util.format('Unknown environment %s', env))
 
-  mergeDefaults(settings, config[env], config.defaults)
+  if (!_.isObject(local))
+    local = {}
+
+  mergeDefaults(settings, local, config[env], config.defaults)
 
   return settings