The old struct config_param remains only for top-level string options.

Since version 2.32, g_thread_init() is deprecated and a no-op.  Let's
upgrade that (optional) dependency so we can remove all those
g_thread_init() calls.

Use a listener interface instead of GlobalEvents.

Passing a void pointer is unsafe.

Avoid GLib.

Prepare for adding state.

Replaces GLib's GError.

Deprecated.

This plugin is horrible code, I mean it.  Last year, I tried hard to
fix it, but I figured would take less time to do a full rewrite.
Given that I don't even have any device that supports RAOP, I can't do
that properly.  After 16 months, nobody volunteered for fixing it.
Hereby, I delete it, because having no RAOP plugin is better than
having this mess.  Sorry.

The other audio_format attributes are not used.

Provide _lock() and _unlock() to wrap all accesses from the mixer
plugin.