Add First Class Closure rules

[Crell]

Not much else to say here. It's pretty basic, and that's a good thing.

[KorvinSzanto]

This looks good to me, I can't help but feel like this belongs in the operators section but I don't really know that the ... here would be an operator.

[Crell]

It's not really an operator. It's really its own "thing". If anything, it's an oddball function call syntax, so I suppose it could go there? I put it in the closures section, but thinking about it, putting it in the function invocation section could make more sense.

[Crell]

Rebased, and moved to the function/method section. A different subsection order may be better, but I didn't want to move too many existing sections. I defer to the Editor on that question.

[kenguest]

Just to tighten up the text, perhaps "The correct format is foo(...)." would suffice? (Removing the 'That is,' preface.)

[Crell]

It feels like it flows better to me with the connecting clause, but if @KorvinSzanto would favor without it I won't take offense. :-)

[KorvinSzanto]

I prefer it without but I prefer to do the finer editing once the entire doc is closer to being ready so we can try to get a common voice.