R1:0318cadad4c2

Fix two issues with audio macros

Summary:
Fixes T3887. Two issues:

- Macros were generating entirely before the render cache, so audio macros worked fine in previews and the first time the cache was populated, but not afterward.
- Instead, parse them before the cache but drop them in after the cache. Clean up all the file querying, too. This makes cached remarkup generate the correct audio beahviors.
- Safari sends an HTTP request with a "Range" header, and expects a "206 Partial Content"…