Add an aria2 input file generator script

[GalaxySnail]

[jquast]

I don't think I can accept this one, there are downstream distros/re-packagers that have been using the update script, this is an external dependency, and, as a python package we aren't really able to describe "this has an external dependency" (except through conda and stuff), anyway I do appreciate the thought, and, we could maybe implement the same idea in python, to use HEAD & last-modified check to re-download only if newer than file's last modified, if that is what aria2c is for

[GalaxySnail]

This script is only for convenience, update-table.py doesn't depend on it. We can always download files by urllib in update-table.py.

I wrote this script because downloading from unicode.org is too slow at my home, and sometimes connections are not stable. Aria2 is not for last-modified checking, but for multi-connection downloading, progress bar, and it can resume downloading after it was interrupted. If files are already downloaded, update-table.py won't download them by urllib, which is good for me. I thought this script may be helpful for developing, so I created this pull request.

[jquast]

I use retry operators and add optional argument not to check HEAD of any file for re-fetch before processing in https://github.com/jquast/wcwidth/pull/61