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

load_avg.c

@@ -0,0 +1,17 @@
+#include <err.h>
+#include <stdlib.h>
+
+#include "util.h"
+
+const char *
+load_avg(const char *fmt)
+{
+	double avgs[3];
+
+	if (getloadavg(avgs, 3) < 0) {
+		warnx("Failed to get the load avg");
+		return NULL;
+	}
+
+	return bprintf(fmt, avgs[0], avgs[1], avgs[2]);
+}