Add support for small-caps font-variant.

Ref: 2554.
Add #[jstraceable] syntax extension
Add fixme comment for future work, make scale factor a constant.
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.
Merge pull request #3459 from glennw/small-caps

Add support for small-caps font-variant.
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
layout: Float table wrappers directly instead of generating a block
wrapper around them.

Fixes Wikipedia tables leaking out.

Along the way, I refactored tables' width calculation significantly.
This was necessary in order to properly handle floated tables, as some
of the logic had to be ported over from block flows.