Was converted to reStructuredText / Sphinx in commit
8a689e68

Migrating from DocBook to Sphinx.  Editing XML is really too
cumbersome.

This way, IsFileNotFound() can detect status 404.

Allows callers to extract the NFS error code.

Make all uses of MusicChunk safe.

This adds a bit of overhead, but also adds flexibility to the API,
because arbitrary triggers may be invoked from that virtual method
implementation, not just Cond::signal().

The motivation for this is to make the handlers more dynamic, for the
upcoming buffering class utilizing ProxyInputStream.

This is not a plugin.

Documentation will follow soon.