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

.github/workflows/action.yml

@@ -40,6 +40,12 @@ jobs:
           node-version: '14'
       - run: npm ci
       - run: npm test
+      - name: .tool-versions test
+        id: setup-beam
+        uses: ./
+        with:
+          version-file: __tests__/.tool-versions
+          version-type: strict
 
   unit_tests_windows:
     name: Unit tests (Windows)