Ease consumption by means of .tool-versions (#159)

* Ease consumption by means of .tool-versions

* Update as per self-review

* Update as per self-review

* Act on CI results

* Act on CI results

* Act on CI results

This value is check by code, in any case

* Act on CI results

* Act on CI results

* Act on CI results

It appears we can't install Elixir twice on Windows, but can
on Ubuntu; this is outside the scope of this branch's context
so I won't fix it now

* Tweak visual consumption elements

* Ease potential future maintenance and/or update

.gitignore

@@ -1,2 +1,3 @@
 node_modules/**
 dist/.github/workflows
+__tests__/.tool-versions