Fix release process

Fail when source-file(s) don't exist.

This closes skx#18.

Merge pull request skx#17 from skx/16-github-actions

16 GitHub actions

Updated tests to avoid running missing-script

Don't echo the password when prompting for it.

We've updated to use a library for hiding input typed by the
user, when they're prompted to enter their sudo-password.

If this is new:

     go get golang.org/x/crypto/ssh/terminal

This closes skx#14.

Brief overview of puppet-summary

Document R/O-variables

Added version sub-command

Reinstated missing file

Removed bogus-quote