Move components into dedicated subdirectory

This brings us a lot more tidiness.

components/hostname.c

@@ -0,0 +1,16 @@
+/* See LICENSE file for copyright and license details. */
+#include <err.h>
+#include <unistd.h>
+
+#include "../util.h"
+
+const char *
+hostname(void)
+{
+	if (gethostname(buf, sizeof(buf)) == -1) {
+		warn("hostname");
+		return NULL;
+	}
+
+	return buf;
+}