Add some javadoc for ProgressListener changes.

// FREEBIE

java/src/main/java/org/whispersystems/textsecure/api/TextSecureMessageReceiver.java

@@ -90,6 +90,25 @@ public class TextSecureMessageReceiver {
    * @throws IOException
    * @throws InvalidMessageException
    */
+  public InputStream retrieveAttachment(TextSecureAttachmentPointer pointer, File destination)
+      throws IOException, InvalidMessageException
+  {
+    return retrieveAttachment(pointer, destination, null);
+  }
+
+
+  /**
+   * Retrieves a TextSecure attachment.
+   *
+   * @param pointer The {@link org.whispersystems.textsecure.api.messages.TextSecureAttachmentPointer}
+   *                received in a {@link TextSecureDataMessage}.
+   * @param destination The download destination for this attachment.
+   * @param listener An optional listener (may be null) to receive callbacks on download progress.
+   *
+   * @return An InputStream that streams the plaintext attachment contents.
+   * @throws IOException
+   * @throws InvalidMessageException
+   */
   public InputStream retrieveAttachment(TextSecureAttachmentPointer pointer, File destination, ProgressListener listener)
       throws IOException, InvalidMessageException
   {

java/src/main/java/org/whispersystems/textsecure/api/messages/TextSecureAttachment.java

@@ -83,7 +83,17 @@ public abstract class TextSecureAttachment {
     }
   }
 
+  /**
+   * An interface to receive progress information on upload/download of
+   * an attachment.
+   */
   public interface ProgressListener {
+    /**
+     * Called on a progress change event.
+     *
+     * @param total The total amount to transmit/receive in bytes.
+     * @param progress The amount that has been transmitted/received in bytes thus far
+     */
     public void onAttachmentProgress(long total, long progress);
   }
 }