Deprecate twitter

We further deprecate the use of twitter.

In cases such as historic guidelines and rules, we add
a note about using Mastodon.

In cases where a tweet URL was used, we replace with
an Internet Archive link because twitter has announced
that accounts that are not used for a period of time
will be deleted.

We add a few missing deprecated_twitter information
to the author.numbers and author.cvs files.

We remove references to twitter handles (after making
sure that both author.numbers and author.cvs has the
deprecated_twitter information).  When the "_README.md_"
files have their header information generated by
a tool, such deprecated_twitter data will not be present.

2020/ferguson1/chocolate-cake.md

@@ -182,8 +182,8 @@ bowl can sit in.
 [picture]: cake.jpg
 [http://www.onlineconversion.com/cooking.htm]: http://www.onlineconversion.com/cooking.htm
 [IOCCC and chocolate]: http://www.gomc.com/firstpage/200103068.pdf
-[International Original Chocolate Cake Contest tweet]: https://twitter.com/ilyakurdyukov/status/1290520266087571458?s=20
-[fellow IOCCC winner Ilya Kurdyukov]: https://twitter.com/ilyakurdyukov
+[International Original Chocolate Cake Contest tweet]: https://web.archive.org/web/20200805053007/https://twitter.com/ilyakurdyukov/status/1290520266087571458
+[fellow IOCCC winner Ilya Kurdyukov GitHub]: https://github.com/ilyakurdyukov
 [GitHub]: https://github.com/ilyakurdyukov
 [IOCCC cake source image]: ioccc-cake.jpg
 [chocolates FAQ]: https://www.davidlebovitz.com/chocolate-faqs/