Introduce a basic shared task pool, and use it for image decoding.
Dump the flow tree with println, instead of error
more efficient preorder DOM traversals
auto merge of #3728 : cgaebel/servo/dump-flow-tree-with-println, r=mrobinson

r? @mrobinson
auto merge of #3744 : cgaebel/servo/efficient-preorder-traversal, r=pcwalton

This also tackles some nearby FIXMEs. `traverse_preorder` is used in a LOT of
DOM functions..

r? @pcwalton
auto merge of #3730 : glennw/servo/taskpool, r=pcwalton

r? @pcwalton - Is this the kind of thing you were thinking of in terms of task queue?
added cmake to dependencies in build instructions
Merge pull request #3764 from dherman/dherman-build-instructions

added cmake to dependencies in build instructions
util: Make some minor formatting cleanups to profiling and gfx