官网安装文件下载：
http://download.xamarin.com/XamarinforMac/Mac/xamarin.mac-2.0.1.64.pkg
http://download.xamarin.com/MonoTouch/Mac/monotouch-8.10.1.74.pkg
http://download.xamarin.com/studio/Mac/XamarinStudio-5.9.3.1-0.dmg
http://download.xamarin.com/MonoFrameworkMDK/Macx86/MonoFramework-MDK-4.0.1.44.macos10.xamarin.x86.pkg