Official proportions for Red/System icon, beginnings of document icons

This started out as just a Red/System commit and I decided that since you hadn't merged it I'd just keep throwing things into it.

One notable thing is that it lays out a distinct proportionality for the Red/System logo. As a fringe benefit...you now have a scalable and cleaned up avatar file...in several formats, but here's one for SO chat size:

![New Avatar](https://raw.githubusercontent.com/hostilefork/branding/master/red-system/red-system-color-128x128.png)

Looks better than:

![Old Avatar](http://i.stack.imgur.com/l68fH.png)

I made a favicon for good measure, although I don't have any suggested use ATM:

![Favicon in context](http://i.stack.imgur.com/938JX.png)

As it grew, I included everything I had.  I also spent an evening actually making a prototype of the document icons.  So there are .ICNS files for OS/X...and I learned some things by the end of the process.  Though I thought that my layout in the document prototype was a bit better, I studied the standards and followed what Apple does (and what Google Chrome did, etc) in terms of positioning.

I've sent notice to Mathieu, who was the first to want document icons, to give it a going over and try to come up with good modern Windows .ICO files.  For the moment, Rebol is piggy-backing in there because it's not much overhead to do the build out of those document icons for it too...and breaking that off would be a hassle.  But eventually you could take that out, after things settle and the strategy for the whole set is done.  Just don't want to repeat effort on those document icons in the meantime.