Allow traditional `for` loops

[vrugtehagel]

It'd be neat if we allowed the traditional initialization; condition; afterthought-style loop in Vento, allowing things like

The even items:
{{ for let index = 0; index < items.length; index += 2 }}
  Index {{ index }}, item {{ item[index] }}
{{ /for }}

I feel like this should be doable, given the only allowed loop now must contain of - what do you think? Worth implementing?

[bobrocke]

I would like that, and perhaps others would too, because of the syntax simplification.

{{ for i of Array.from({length: end_index - start_index + 1}, (_, index) => index + start_index) }}
   do stuff
{{ /for}}

is a bit convoluted and messy.

[oscarotero]

For simple things, you can do {{ for index of items.length }}.
But it doesn't allow to customize the condition or afterthought part. So maybe it could be a good addition.