[core] add option to trim file name length with integer

https://github.com/blackjack4494/youtube-dlc/issues/85

youtube_dlc/__init__.py

@@ -390,6 +390,7 @@ def _real_main(argv=None):
         'rejecttitle': decodeOption(opts.rejecttitle),
         'max_downloads': opts.max_downloads,
         'prefer_free_formats': opts.prefer_free_formats,
+        'trim_file_name': opts.trim_file_name,
         'verbose': opts.verbose,
         'dump_intermediate_pages': opts.dump_intermediate_pages,
         'write_pages': opts.write_pages,