CI implementation

[Eriner]

It would be nice to have a CI system to perform both static (think shellcheck, grep-based style linting) and dynamic analysis (run in subshell, check retcode, prompt, function availability/functionality, etc).

Github Actions can be used for the CI. Necessary tooling is still unknown, as it would likely need to be zsh-specific and I'm not aware of any off the top of my head, though I haven't investigated what's available.

One obvious upside to performing testing like this is that we could test varying versions of zsh and catch any is-at-least type bugs, as well as PRs that may subtly break some functionality.

[Eriner]

koalaman/shellcheck#809

[grzesuav]

hi @Eriner , I could help with this by implementing as github actions. The are limited as to image you can use (it is not gitlab-ci) but shellcheck should be no problem.

I noticed that you stared to follow semantic releasing, maybe this is something which also could be automated.