Split into multiple files

For multiple reasons the program is now split:
- Make future porting to OpenBSD easier
- Assign header includes to individiual functions
- Make future program extensions easier
- Recompile only changed parts

volume.c

@@ -0,0 +1,42 @@
+#include <err.h>
+#include <fcntl.h>
+#include <sys/soundcard.h>
+#include <sys/ioctl.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "util.h"
+
+const char *
+vol_perc(const char *card)
+{
+	unsigned int i;
+	int v, afd, devmask;
+	char *vnames[] = SOUND_DEVICE_NAMES;
+
+	afd = open(card, O_RDONLY | O_NONBLOCK);
+	if (afd == -1) {
+		warn("Cannot open %s", card);
+		return NULL;
+	}
+
+	if (ioctl(afd, SOUND_MIXER_READ_DEVMASK, &devmask) == -1) {
+		warn("Cannot get volume for %s", card);
+		close(afd);
+		return NULL;
+	}
+	for (i = 0; i < LEN(vnames); i++) {
+		if (devmask & (1 << i) && !strcmp("vol", vnames[i])) {
+			if (ioctl(afd, MIXER_READ(i), &v) == -1) {
+				warn("vol_perc: ioctl");
+				close(afd);
+				return NULL;
+			}
+		}
+	}
+
+	close(afd);
+
+	return bprintf("%d", v & 0xff);
+}