Fix some typos, broken links and other issues in extension docs

chrome/common/extensions/api/management.json

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 [
   {
     "namespace":"management",
     "types": [
       {
         "id": "IconInfo",
@@ skipping 303 matching lines @@
         ]
       },
       {
         "name": "onEnabled",
         "description": "Fired when an app or extension has been enabled.",
         "type": "function",
         "parameters": [{"name": "info", "$ref":"ExtensionInfo"}]
       },
       {
         "name": "onDisabled",
-        "description": "Fired when an app or extension has been disabled",
+        "description": "Fired when an app or extension has been disabled.",
         "type": "function",
         "parameters": [{"name": "info", "$ref":"ExtensionInfo"}]
       }
     ]
   }
 ]