调用Native Plugin

使用C/C++生成的库，调用方法如下

// Native Plugin 中声明的函数
float FooPluginFunction () { return 5.0F; } 

using UnityEngine;
    using System.Runtime.InteropServices;

    class SomeScript : MonoBehaviour {

       #if UNITY_IPHONE

       // On iOS plugins are statically linked into
       // the executable, so we have to use __Internal as the
       // library name.
       [DllImport ("__Internal")]

       #else

       // Other platforms load plugins dynamically, so pass the name
       // of the plugin's dynamic library.
       [DllImport ("PluginName")]

       #endif

       private static extern float FooPluginFunction ();

       void Awake () {
          // Calls the FooPluginFunction inside the plugin
          // And prints 5 to the console
          print (FooPluginFunction ());
       }
    }