Uses the `wdiff` tool as a diffing engine. This produces an output that is more useful for copy-editing tasks. This wdiff comparison is then processed in a way that is aware of markdown formatting. The resulting output attempts to show differences of copy within the final document format (rather than differences of format).
The markdown-sensitive processing of the wdiff comparison is at `server/components/wdiff/index.js`, for the curious.
