* Rewrites the demo documentation to be clearer, accurate, and moves it to our documentation tree.
* Improvements to the demo scripts:
* `clean.sh` now runs `stop.sh` first to avoid zombie processes.
* Uses more modern Synapse configuration (and removes some obsolete configuration).
* Consistently use the HTTP ports for server name, etc.
* Remove the `demo/etc` directory and place everything into the `demo/808x` directories.
Our documentation has a history of using a document's name as a way to link to it, such as "See [workers.md]() for details". This makes sense when you're traversing a directory of files, but less sense when the files are abstracted away - as they are on the documentation website.
This PR changes the links to various documentation pages to something that fits better into the surrounding sentence, as you would when making any hyperlink on the web.
