Add basic_fetch and a skeleton http_fetch
Add a basic CORS Cache and a CORS Cache trait
Add a task-based CORS Cache
Some docs
Transmute std::raw::TraitObject rather than (some) custom tuples/structs.

Context:
http://www.mail-archive.com/dev-servo@lists.mozilla.org/msg00867.html

This fixes the known issues, but there might be other places
where we do "bad" transmutes that I haven’t discovered.
Add a canvas create, break script’s dependency on gfx.

The build time on my laptop after touching gfx goes from 1m37s ot 46s.
Merge pull request #3170 from SimonSapin/trait-object-transmute

Transmute std::raw::TraitObject rather than (some) custom tuples/structs
Merge pull request #3141 from Manishearth/fetch-stuff

Some more Fetch and CORS Cache stuff; r=jdm
Merge pull request #3178 from SimonSapin/canvas-crate

Add a canvas create, break script’s dependency on gfx.
Make text decorations be independent display items.

The goal it to avoid having too much layout logic (which gets more complex in vertical text) in gfx code.
Implement sideways text.