Subscriptions: How to "Listen" for Events and What to do ...

[nelsonic]

In order to have "Event Listeners" (so users can hit the [Enter] Key to create a Todo Item #55)
We need to add "Subscriptions" to Elm(ish).
see: https://www.elm-tutorial.org/en/03-subs-cmds/01-subs.html

Todo

• investigate/research if we need to register events each time the DOM is re-rendered
• write a test for subscriptions ... e.g:
  • [Up] & [Down] keyboard key press increases/decreases the counter.
• add subscriptions parameter to mount function
• invoke the subscriptions in mount depending on the outcome of initial research

required for: #55