Iteration over Set's with v-for

[msalestream]

I was building something the other day with a set, and noticed I couldn't seem to iterate over it with a v-for.

Example (Use Modern Browser):
https://jsfiddle.net/n9b9g0t0/3/

I understand Set's do behave a little differently then plain objects and array's, but I do see a massive benefit in adding them into v-for iteration. I am open to writing this addition if deemed useful.

[simplesmiler]

Closed if favor of #2410