Style play.rust-lang.org similarly to www.rust-lang.org, etc.

[brson]

Currently at http://playtest.rust-lang.org

This needs to fit in with the rest of our stuff. Source is yonder: https://github.com/rust-lang/rust-playpen

cc #6916

[brson]

cc @adrientetar @thehydroimpulse

[kud1ing]

This should also mention which version of Rust this is.

[thestinger]

@kud1ing: There's a version selection drop-down menu.

[kud1ing]

@thestinger Ok.

[noamraph]

I think that the output and code should appear side by side. In the current design, all the right part of my screen is used by the area in the code box which is after 80 columns (that is, should be blank), and in order to see the result I have to scroll.

[huonw]

@noamraph see rust-lang/rust-playpen#5.

[thestinger]

Closing in favour of rust-lang/rust-playpen#41. There's no point of having an issue open here too. There isn't really a consistent style to copy anyway.