This continues #139

Changes are on the upgrade branch

Changelog:

• Upstream: 6e0d996...4558df3
• Servo fixups:
  • Use git version of cssparser cf5ca8f
  • Revert markup5ever bump (Bump markup5ever version #141) (Servo hasn't upgraded yet and corresponding html5ever version have been yanked) This fixup has now been removed (markup5ever bump reinstated) as the issue with html5ever has been resolved and servo has been updated to use the new version).

Servo PR: servo/servo#35990