Impelemented zooming and slightly better scrolling.
Merge with pcwalton's updated branch
Changed texturing mode to LINEAR for better zooming
Add initial support for the line-height property. Line height is only based on the tallest box in each line and does not factor in the vertical-alignment. Improves whitespace handling by passing the whitespace state between function invocations.
Merge onto mozilla/servo master
Merge branch 'master' of https://github.com/mozilla/servo
decouple script from compositor
communicate via layout
refactor channel wrappers from *Task --> *Chan

fix merge fallout
fixed docstring for create_compositor_task
*Chan.send() convenience functions
profiler refactor to print every period if new data has arrived
Add initial support for the line-height property. Line height is only based on the tallest box in each line and does not factor in the vertical-alignment. Improves whitespace handling by passing the whitespace state between function invocations.
refactor compositor interfaces \--> RenderListener + ScriptListener; AttachCompositorMsg added to render_task::Msg

updated to reflect comments
auto merge of #517 : tkuehn/servo/master, r=metajack

communicate via layout
refactor channel wrappers from *Task --> *Chan
Propagate debug flag in Makefiles.
Adding renderer drawing category to profiler.
Merge branch 'master' of https://github.com/mozilla/servo
Warning police.
Refactor renderer into single function.

This removes the task per tile rendering and instead renders tiles
serially. This also unwraps the rendering into a single function so that it's
much clearer.
Add quadtree implementation
Add LRU cache and use it for fonts and font groups