Support CSON config file

Use ~/.atom/config.cson as the new default when no
config file exists.

~/.atom/config.json is still the default if they both
exist.

src/app/config.coffee

@@ -3,7 +3,6 @@ _ = require 'underscore'
 EventEmitter = require 'event-emitter'
 
 configDirPath = fs.absolute("~/.atom")
-configJsonPath = fs.join(configDirPath, "config.json")
 userInitScriptPath = fs.join(configDirPath, "user.coffee")
 bundledPackagesDirPath = fs.join(resourcePath, "src/packages")
 bundledThemesDirPath = fs.join(resourcePath, "themes")
@@ -27,6 +26,8 @@ class Config
       core: _.clone(require('root-view').configDefaults)
       editor: _.clone(require('editor').configDefaults)
     @settings = {}
+    @configFilePath = fs.resolveExtension(fs.join(configDirPath, 'config'), ['json', 'cson'])
+    @configFilePath ?= fs.join(configDirPath, 'config.cson')
 
   load: ->
     @loadUserConfig()
@@ -35,8 +36,8 @@ class Config
     atom.loadPackages()
 
   loadUserConfig: ->
-    if fs.exists(configJsonPath)
-      userConfig = JSON.parse(fs.read(configJsonPath))
+    if fs.exists(@configFilePath)
+      userConfig = fs.readObject(@configFilePath)
       _.extend(@settings, userConfig)
 
   get: (keyPath) ->
@@ -77,7 +78,7 @@ class Config
     @trigger 'updated'
 
   save: ->
-    fs.write(configJsonPath, JSON.stringify(@settings, undefined, 2) + "\n")
+    fs.writeObject(@configFilePath, @settings)
 
   requireUserInitScript: ->
     try

src/stdlib/fs.coffee

@@ -188,6 +188,14 @@ module.exports =
     else
       JSON.parse(contents)
 
+  writeObject: (path, object) ->
+    if @extension(path) is '.cson'
+      CSON = require 'cson'
+      content = CSON.stringify(object)
+    else
+      content = JSON.stringify(object, undefined, 2)
+    @write(path, "#{content}\n")
+
   readPlist: (path) ->
     plist = require 'plist'
     object = null