Fix style in `CharacterData`.
Fix code style in DOMParser
Remove ancient `net.rs`
servo: Refactor the `Flow` type to save memory and allow upcasting and downcasting more naturally
layout: Document the root flow.
util: Add a new `tree` module to avoid duplicating pointer stitching.

Add some basic support to AbstractNode for it.
dom: Document the node structure better and remove the node pointer stitching routines
layout: Port the flow tree over to the new generic tree functions
layout: Remove duplicate methods from flows
dom: Remove duplicate methods from the DOM node type
layout: Refactor inline layout a bit
servo: Rename `as_immutable_node` to `as_imm_node` and `as_mutable_node` to `as_mut_node`
Merge pull request #416 from pcwalton/refactor-flow

Refactor flow