Merge pull request #22 from SimonSapin/master

Upgrade rust and some clean-ups. r=metajack
fmt! -> format!
Upgrade Rust
Merge branch 'rust-upgrade' of https://github.com/kmcallister/rust-cssparser
Add an incomplete CSS serializer.

Serialization is considered correct if it maintains the invariant:

  parse(serialize(parse(text))) == parse(text)

for any text (Unicode string.)
This is not the case of this code yet (see #24),
but it’s good enough for error reporting in Servo.
De-duplicate identifier serializer logic.
Merge pull request #25 from SimonSapin/serializer

Add an incomplete CSS serializer.
Disable incorrect serializer fixups.
Merge pull request #28 from SimonSapin/serializer

Disable incorrect serializer fixups.
Warning police.
New visibility rules: only export what is meant to be public.
Merge pull request #29 from SimonSapin/private

New visibility rules: only export what is meant to be public.