Add #[jstraceable] syntax extension
Handle null strings in Namespace::new.

This also avoids a string copy in the rare case of an unrecognized namespace.
Remove redundant into_string() calls.
Add untraceable! macro
layout: Implement `white-space: nowrap`.

Improves the Reddit header.
Use JSTraceable everywhere
Update docs
Merge pull request #3466 from Ms2ger/into_string

Remove redundant into_string() calls.; r=jdm
Merge pull request #3458 from pcwalton/whitespace-nowrap

layout: Implement `white-space: nowrap`.
Address review comments
Merge pull request #3465 from Ms2ger/ns

Handle null strings in Namespace::new.
Merge pull request #3468 from Manishearth/jstraceable

Replace our usage our Encodable with JSTraceable; r=jdm