Added a custom chunksize to the GetContentFile method. (#50)

* Added a custom chunksize to the GetContentFile method.

* Fixed formatting with black

Author: TanukiAI

pydrive2/files.py

@@ -308,7 +308,12 @@ def GetContentString(
 
     @LoadAuth
     def GetContentFile(
-        self, filename, mimetype=None, remove_bom=False, callback=None
+        self,
+        filename,
+        mimetype=None,
+        remove_bom=False,
+        callback=None,
+        chunksize=DEFAULT_CHUNK_SIZE,
     ):
         """Save content of this file as a local file.
 
@@ -320,6 +325,8 @@ def GetContentFile(
     :type remove_bom: bool
     :param callback: passed two arguments: (total trasferred, file size).
     :type param: callable
+    :param chunksize: chunksize in bytes (standard 100 MB(1024*1024*100))
+    :type chunksize: int
     :raises: ApiRequestError, FileNotUploadedError
     """
         files = self.auth.service.files()
@@ -328,7 +335,9 @@ def GetContentFile(
             raise FileNotUploadedError()
 
         def download(fd, request):
-            downloader = MediaIoBaseDownload(fd, self._WrapRequest(request))
+            downloader = MediaIoBaseDownload(
+                fd, self._WrapRequest(request), chunksize=chunksize
+            )
             done = False
             while done is False:
                 status, done = downloader.next_chunk()