Add new ParseFile download api

Parse/src/main/java/com/parse/GetDataCallback.java

@@ -37,3 +37,4 @@ public interface GetDataCallback extends ParseCallback2<byte[], ParseException>
   @Override
   public void done(byte[] data, ParseException e);
 }
+

Parse/src/main/java/com/parse/GetDataStreamCallback.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2015-present, Parse, LLC.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+package com.parse;
+
+import java.io.InputStream;
+
+/**
+ * A {@code GetDataStreamCallback} is used to run code after a {@link ParseFile} fetches its data on
+ * a background thread.
+ * <p/>
+ * The easiest way to use a {@code GetDataStreamCallback} is through an anonymous inner class.
+ * Override the {@code done} function to specify what the callback should do after the fetch is
+ * complete. The {@code done} function will be run in the UI thread, while the fetch happens in a
+ * background thread. This ensures that the UI does not freeze while the fetch happens.
+ * <p/>
+ * <pre>
+ * file.getDataStreamInBackground(new GetDataStreamCallback() {
+ *   public void done(InputSteam input, ParseException e) {
+ *     // ...
+ *   }
+ * });
+ * </pre>
+ */
+public interface GetDataStreamCallback extends ParseCallback2<InputStream, ParseException> {
+  /**
+   * Override this function with the code you want to run after the fetch is complete.
+   *
+   * @param input
+   *          The data that was retrieved, or {@code null} if it did not succeed.
+   * @param e
+   *          The exception raised by the fetch, or {@code null} if it succeeded.
+   */
+  @Override
+  public void done(InputStream input, ParseException e);
+}

Parse/src/main/java/com/parse/GetFileCallback.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright (c) 2015-present, Parse, LLC.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+package com.parse;
+
+import java.io.File;
+
+/**
+ * A {@code GetFileCallback} is used to run code after a {@link ParseFile} fetches its data on
+ * a background thread.
+ * <p/>
+ * The easiest way to use a {@code GetFileCallback} is through an anonymous inner class.
+ * Override the {@code done} function to specify what the callback should do after the fetch is 
+ * complete. The {@code done} function will be run in the UI thread, while the fetch happens in a
+ * background thread. This ensures that the UI does not freeze while the fetch happens.
+ * <p/>
+ * <pre>
+ * file.getFileInBackground(new GetFileCallback() {
+ *   public void done(File file, ParseException e) {
+ *     // ...
+ *   }
+ * });
+ * </pre>
+ */
+public interface GetFileCallback extends ParseCallback2<File, ParseException> {
+  /**
+   * Override this function with the code you want to run after the fetch is complete.
+   *
+   * @param file
+   *          The data that was retrieved, or {@code null} if it did not succeed.
+   * @param e
+   *          The exception raised by the fetch, or {@code null} if it succeeded.
+   */
+  @Override
+  public void done(File file, ParseException e);
+}