Add shell escaping

[Jongy]

• Not implemented for the pgrep command in pgrep-mode - gonna trust the user on that :)
• Not implemented for the version_cmd because it's not needed there (only numbers are encoded, not strings)
• Not escaping symbol names in get_symbol_offset because they are constants throughout the project.

I tested it with a PHP binary I put in /tmp/php''$(echo > yyy). Works like a charm (and no yyy file created in cwd, but neither does in master).
Also tested with /tmp/php$(echo > abc), no abc file created in cwd.
On master - both don't work & abc is created.

Also dropped a small commit that fixes a missing s(n)printf overflow (like 3120b8d)

Closes: #81

[adsr]

Thank you @Jongy. This is on my backlog to review.

[adsr]

Going to close and re-open this PR to hopefully trigger the new GitHub Actions CI.

[Jongy]

Thanks @adsr !