initial sound feature

This replaces the many sets of the corresponding packages
wandering all over pkglists, features and configurations;
the interface should be rather well-defined by now.

features.in/sound/README

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+Эта фича добавляет поддержку аудиоподсистемы (как ядерную,
+если не включена в kernel-image, так и утилиты).

features.in/sound/config.mk

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++pulse: use/sound/pulse; @:
+
+# common ALSA based part
+use/sound:
+	@$(call add_feature)
+	@$(call add,THE_KMODULES,alsa)
+	@$(call add,THE_PACKAGES,amixer alsa-utils aplay)
+
+# "bare" ALSA (which is good enough for many of us) with persistent levels
+use/sound/alsa: use/sound
+	@$(call add,THE_PACKAGES,udev-alsa)
+
+# PulseAudio (useful for per-app levels, dynamic devices and networked sound)
+use/sound/pulse: use/sound
+	@$(call add,THE_LISTS,pulseaudio)

pkg.in/lists/pulseaudio

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+pulseaudio-daemon
+
+pulseaudio-utils
+pavucontrol
+
+alsa-plugins-pulse