Add `shell_ssh` module

[ZanyMonk]

Requires #173 to be merged first.

• [x] Add :shell_ssh command
  • [x] Add ssh2_connect()-based vector: php
  • [x] Add paramiko-based vector: py.paramiko
  • [x] Add pexpect-based vector: py.pexpect
  • [x] Add subprocess.Popen()-based vector : py.subprocess
• [x] Add unit tests
• [x] Insure tests are running on both PHP 7 and 8