Handle expect scripts

[mcandre]

As an expect developer, I want stank to recognize expect scripts as distinct from POSIXy shell scripts, so that I do not apply shell linters to non-shell scripts.

UNIX expect scripts are gently encouraged to omit the file extension, or else use *.sh. Such an extension would probably lead the stank system to conclude that the script is intended to be a POSIXy script, though of course the expect grammar is not POSIX shell but its own thing.

The stank system should handle these scripts by:

• [ ] No longer treating .sh file extensions as 100% conclusive that a script is POSIXy.
• [x] Treat expect shebang interpreter as non-POSIXy.
• [ ] Add a -expect rule to funk, off by default, that recommends expect scripts to use the extension .expect, in order to more easily disambiguate for both humans and machines, between true POSIXy shell scripts and expect scripts.
• [ ] Copy expecto-patronum from mcandre/vagrant-macos-fink to examples/.
• [ ] Demo an example prompting script and expect runner script in mcandre/toys/expect.