[openssl/openssl] ec3653: Add initial demo-driven design demos

[Hugo Landau]

  Branch: refs/heads/master
  Home:   https://github.openssl.org/openssl/openssl
  Commit: ec36534cbbf57999b90cbb36404d9daa599a9ae4
      https://github.openssl.org/openssl/openssl/commit/ec36534cbbf57999b90cbb36404d9daa599a9ae4
  Author: Hugo Landau <hlandau at openssl.org>
  Date:   2022-06-24 (Fri, 24 Jun 2022)

  Changed paths:
    A doc/designs/ddd/Makefile
    A doc/designs/ddd/README.md
    A doc/designs/ddd/WINDOWS.md
    A doc/designs/ddd/ddd-01-conn-blocking.c
    A doc/designs/ddd/ddd-02-conn-nonblocking.c
    A doc/designs/ddd/ddd-03-fd-blocking.c
    A doc/designs/ddd/ddd-04-fd-nonblocking.c
    A doc/designs/ddd/ddd-05-mem-nonblocking.c
    A doc/designs/ddd/ddd-06-mem-uv.c
    M util/markdownlint.rb

  Log Message:
  -----------
  Add initial demo-driven design demos

Reviewed-by: Paul Dale <pauli at openssl.org>
Reviewed-by: Tomas Mraz <tomas at openssl.org>
(Merged from https://github.com/openssl/openssl/pull/17991)