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

uptime.c

@@ -0,0 +1,17 @@
+#include <sys/sysinfo.h>
+
+#include "util.h"
+
+const char *
+uptime(void)
+{
+	struct sysinfo info;
+	int h = 0;
+	int m = 0;
+
+	sysinfo(&info);
+	h = info.uptime / 3600;
+	m = (info.uptime - h * 3600 ) / 60;
+
+	return bprintf("%dh %dm", h, m);
+}