sound examples: Simplify audio example

[christos]

Summary

• Merge ossinit.h and basic.c.
• Rename basic.c to audio.c.
• Use err(3) instead of fprintf(3) + exit(3).
• Some style(9) improvements.

Sponsored by: The FreeBSD Foundation
MFC after: 2 days

[christos]

Add ossinit.h removal to ObsoleteFiles.inc.

[christos]

Add basic.c rename to ObsoleteFiles.inc as well.

[dev_submerge.ch]

I suppose the original idea by @meka_tilda.center was to implement another example using mmap, at least there's code fragments for that. What's the plan regarding a mmap example?

[christos]

In D46307#1057113, @dev_submerge.ch wrote:

I suppose the original idea by @meka_tilda.center was to implement another example using mmap, at least there's code fragments for that. What's the plan regarding a mmap example?

Here I simply re-arranged and cleaned up some parts. I think the mmap example should be added in a separate patch.

[meka_tilda.center]

In D46307#1057113, @dev_submerge.ch wrote:

I suppose the original idea by @meka_tilda.center was to implement another example using mmap, at least there's code fragments for that. What's the plan regarding a mmap example?

To be honest, at the time of writing those examples I didn't know much about FreeBSD audio. As a matter of fact, that was the reason I wrote them: I wanted to learn and write it down for others. So, thank you, Christos, for improving it. Where I hit the wall is mmap mode and kqueue example, because cuse (hence, virtual_oss) has kqueue handler, but kernel OSS doesn't. What I'm trying to say is that I wrote down in those examples as I learned, so no wonder there are traces of mmap support.