add 'download' option (#220)

gallery_dl/job.py

@@ -307,7 +307,10 @@ class DownloadJob(Job):
         self.pathfmt = util.PathFormat(self.extractor)
         if keywords:
             self.pathfmt.set_directory(keywords)
+
         self.sleep = self.extractor.config("sleep")
+        if not self.extractor.config("download", True):
+            self.download = lambda x: True
 
         skip = self.extractor.config("skip", True)
         if skip:

gallery_dl/option.py

@@ -205,6 +205,11 @@ def build_parser():
         help=("Do not set file modification times according to "
               "Last-Modified HTTP response headers")
     )
+    downloader.add_argument(
+        "--no-download",
+        dest="download", nargs=0, action=ConfigConstAction, const=False,
+        help=("Do not download any files")
+    )
     downloader.add_argument(
         "--no-check-certificate",
         dest="verify", nargs=0, action=ConfigConstAction, const=False,