Implement save, share image from archive

app/src/main/java/com/hippo/Native.java

@@ -18,8 +18,12 @@
 
 package com.hippo;
 
+import java.io.FileDescriptor;
+
 public class Native {
     public static void initialize() {
         System.loadLibrary("ehviewer");
     }
+
+    public static native int getFd(FileDescriptor fd);
 }