Insert markers into output SSML for navigation.

Extensively refactor to use the CSS engine's counters implementation.

Output audio cues in live speech.

Turned out I was overcomplicating things, all I needed to do was use file paths not URIs.
eSpeak NG handled it from there.

Link audio cue associates closer to suffix than prefix.

Fix links to audio cue.

Upload Types modules, & useragent stylesheet with audio cues.

Prevent websites (and userstyles) from overriding the link audio cue.