Merge autogradpp into PyTorch (#7074)

* Dump autogradpp into PyTorch

* Fixed up CMake for autogradpp/C++ API

* Made cereal a submodule

* Change search location of autogradpps mnist directory

* Add test_api to CI

* Download MNIST from the internet instead of storing in repo

* Fix warnings

tools/download_mnist.py

@@ -0,0 +1,81 @@
+from __future__ import division
+from __future__ import print_function
+
+import argparse
+import gzip
+import os
+import sys
+import urllib
+
+try:
+    from urllib.error import URLError
+    from urllib.request import urlretrieve
+except ImportError:
+    from urllib2 import URLError
+    from urllib import urlretrieve
+
+RESOURCES = [
+    'train-images-idx3-ubyte.gz',
+    'train-labels-idx1-ubyte.gz',
+    't10k-images-idx3-ubyte.gz',
+    't10k-labels-idx1-ubyte.gz',
+]
+
+
+def report_download_progress(chunk_number, chunk_size, file_size):
+    if file_size != -1:
+        percent = min(1, (chunk_number * chunk_size) / file_size)
+        bar = '#' * int(64 * percent)
+        sys.stdout.write('\r0% |{:<64}| {}%'.format(bar, int(percent * 100)))
+
+
+def download(destination_path, url):
+    if os.path.exists(destination_path):
+        print('{} already exists, skipping ...'.format(destination_path))
+    else:
+        print('Downloading {} ...'.format(url))
+        try:
+            urlretrieve(
+                url, destination_path, reporthook=report_download_progress)
+        except URLError:
+            raise RuntimeError('Error downloading resource!')
+        finally:
+            # Just a newline.
+            print()
+
+
+def unzip(zipped_path):
+    unzipped_path = os.path.splitext(zipped_path)[0]
+    if os.path.exists(unzipped_path):
+        print('{} already exists, skipping ... '.format(unzipped_path))
+        return
+    with gzip.open(zipped_path, 'rb') as zipped_file:
+        with open(unzipped_path, 'wb') as unzipped_file:
+            unzipped_file.write(zipped_file.read())
+            print('Unzipped {} ...'.format(zipped_path))
+
+
+def main():
+    parser = argparse.ArgumentParser(
+        description='Download the MNIST dataset from the internet')
+    parser.add_argument(
+        '-d', '--destination', default='.', help='Destination directory')
+    options = parser.parse_args()
+
+    if not os.path.exists(options.destination):
+        os.makedirs(options.destination)
+
+    try:
+        for resource in RESOURCES:
+            path = os.path.join(options.destination, resource)
+            url = 'http://yann.lecun.com/exdb/mnist/{}'.format(resource)
+            download(path, url)
+            unzip(path)
+    except KeyboardInterrupt:
+        print('Interrupted')
+
+    print('Done')
+
+
+if __name__ == '__main__':
+    main()