Returntypehinting RFC

RFC'd by @morrisonlevi

PR'd for review + CI

https://wiki.php.net/rfc/returntypehinting
On Wed, Aug 20, 2014 at 11:42 PM, Dmitry Stogov
<notifications@github.com> wrote:
>
> I suppose the syntax with column came from Virt family languages (Pascal, Modula, Ada, etc). It looks natural for me and it shouldn't make any grammar conflicts with ternary operator.

Yes, the syntax is precedented in these languages and others. It's a
common way to denote types of things in general. One language of
interest is Hack which also uses a colon here.

In regards to the position section: I didn't put symbols in there
because many languages put return types there but use different
symbols for it. I was just demonstrating common positions, not syntax
itself.