Add possibility to use a custom program to play sound files.

[ShadowMitia]

This PR allows for custom programs to be set on systems that don't have "afplay" or "aplay" installed.
This can be set in the user's configuration files manually or through M-x customize.

This should close #13.

[ShadowMitia]

Also helps with #16

[Anton-Latukha]

In PR you assume that person has PulseAudio.

I have, but some people really, really don't.

aplay seems was, and is the standard.

If person has PulseAudio installed => Pulse requires ALSA to be installed.
PulseAudio sets itself as default ALSA device. So there is no sense to limit users to paplay, that is Pulse utility only.

If you use aplay, you automatically use PulseAudio, if Pulse was installed. If Pulse is not present - it uses default ALSA audio device. And it can be ALSA, PipeWire, of Jack1, Jack2, OSS, NAS or whatever sound routing configured as default ALSA device.

[ShadowMitia]

I assume that Pulseaudio is the default on most systems, I could be wrong on that and don't mind changing.

But the whole point of this PR is to be able to change what plays sound easily for the user, so the default should be something that's common to most systems.

Like I said in the issue, I didn't even have aplay installed, but maybe that was just a fluke on my system.

Could you share some documentation that shows how aplay automatically chooses the output system? I have few experience in sound systems, and I was adamant aplay was ALSA only. I would like to read up more on that.

[Anton-Latukha]

AFAIK aplay on Arch probably is still provided in alsa-tools.

It is debatable argument why paplay is on your system and aplay is not, while your system both uses PulseAudio and ALSA at the same time.

It can be that paplay just got packaged into the pulse package, while alsa maintainer decided to split it into alsa-tools. In that case the, on Arch, the alsa maintainer seems more in line with the distribution ideas. Or you have pulse-tools installed. It depends on the distribution.

I am really up for good migration from dependency of everything on ALSA. They done a big mistake in the base design (it is forgotten story), that PulseAudio also trying to cover up so hard. But for nearest, foreseen, years everything would still run on ALSA, so targeting it seems logical.

I am not really strongly on left or right here, it can stay also as it is or whatever.

[zellerin]

Just curious, why simply replacing selectric-make-sound with built-in play-sound-file does not work?