Add --overwrite option (#182)

* Add overwrite option

* Fix tests

* address changes requested

core/internals.py

@@ -62,6 +62,10 @@ def get_arguments():
     parser.add_argument(
         '-f', '--folder', default=(os.path.join(sys.path[0], 'Music')),
         help='path to folder where files will be stored in')
+    parser.add_argument(
+        '--overwrite', default='prompt',
+        help='change the overwrite policy',
+        choices={'prompt', 'force', 'skip'})
     parser.add_argument(
         '-i', '--input-ext', default='.m4a',
         help='prefered input format .m4a or .webm (Opus)')