Use new Mozilla 'sandstone' visual style for rust-lang.org

[brson]

https://www.mozilla.org/b/en-US/sandstone/

They don't appear to provide any guidance on when this style should be used, but it is probably appropriate for rust-lang.org.

[bstrie]

Noticed that the "page template" and "subpage template" download buttons on that page don't point to anything. Not sure where to report that... perhaps you could forward this information to the person in charge of that page?

[graydon]

Not sure I agree on this. I've been pretty intentional about positioning rust as a community that isn't necessarily a subset of mozilla's community. Lots of people have a stake in language development who don't participate in or necessarily care about the mozilla project.

[brson]

@graydon Your point is persuasive.