add snd_device_name_hint() function and initial implementation

- add snd_device_name_hint() and snd_device_name_free_hint() functions
- add snd_ctl_iface_conf_name() functions
- do not accept parameters for the plugin definition without @args section
- add defaults.pcm.dmix.card/device and dsnoop.card/device definitions
- add hints for HDA-Intel.conf, pcm/dmix.conf, pcm/dsnoop.conf and alsa.conf
- add test/namehint test utility
- doxygen related cleanups

test/namehint.c

@@ -0,0 +1,28 @@
+#include "../include/asoundlib.h"
+#include <err.h>
+
+int main(int argc, char *argv[])
+{
+	const char *iface = "pcm";
+	snd_ctl_elem_iface_t niface;
+	char **hints, **n;
+	int err;
+
+	if (argc > 1)
+		iface = argv[1];
+	for (niface = 0; niface < SND_CTL_ELEM_IFACE_LAST; niface++)
+		if (strcmp(snd_ctl_iface_conf_name(niface), iface) == 0)
+			break;
+	if (niface > SND_CTL_ELEM_IFACE_LAST)
+		errx(1, "interface %s dnoes not exist", iface);
+	err = snd_device_name_hint(-1, niface, &hints);
+	if (err < 0)
+		errx(1, "snd_device_name_hint error: %s", snd_strerror(err));
+	n = hints;
+	while (*n != NULL) {
+		printf("%s\n", *n);
+		n++;
+	}
+	snd_device_name_free_hint(hints);
+	return 0;
+}