add agetline, separate estrtod to util

Signed-off-by: Hiltjo Posthuma <hiltjo@codemadness.org>

util/estrtod.c

@@ -0,0 +1,18 @@
+/* See LICENSE file for copyright and license details. */
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "../util.h"
+
+double
+estrtod(const char *s)
+{
+	char *end;
+	double d;
+
+	d = strtod(s, &end);
+	if(end == s || *end != '\0')
+		eprintf("%s: not a real number\n", s);
+	return d;
+}