Servo 0.0.6 speeds up layout, enhances DevTools, and starts accessibility work

Servo 0.0.6 delivers major layout speedups with incremental rendering for box and fragment trees, improving both performance and memory efficiency. Developer tools gain new debugging capabilities including script pausing and stepping, revisions to Inspector, and enhanced Console previews. Initial accessibility support is under development, enabling webviews to provide accessibility trees for integration by embedders. The release also updates the embedding API, refines web platform features, adds new HTML and CSS support, and fixes numerous bugs.