Scrap chartorunearr(), introducing utftorunestr()

Interface and function as proposed by cls.

The reasoning behind this function is that cls expressed his
interest to keep memory allocation out of libutf, which is a
very good motive.
This simplifies the function a lot and should also increase the
speed a bit, but the most important factor here is that there's
no malloc anywhere in libutf, making it a lot smaller and more
robust with a smaller attack-surface.

Look at the paste(1) and tr(1) changes for an idiomatic way to
allocate the right amount of space for the Rune-array.

libutf/chartorunearr.c

@@ -1,27 +0,0 @@
-/* See LICENSE file for copyright and license details. */
-#include <stdlib.h>
-#include <string.h>
-
-#include "../util.h"
-#include "../utf.h"
-
-int
-chartorunearr(const char *str, Rune **r)
-{
-	size_t len = strlen(str), rlen, roff, ret = 1, i;
-	Rune s;
-
-	for (rlen = 0, roff = 0; roff < len && ret; rlen++) {
-		ret = charntorune(&s, str + roff, MAX(UTFmax, len - roff));
-		roff += ret;
-	}
-
-	*r = emalloc(rlen * sizeof(Rune) + 1);
-	(*r)[rlen] = 0;
-
-	for (i = 0, roff = 0; roff < len && i < rlen; i++) {
-		roff += charntorune(&(*r)[i], str + roff, MAX(UTFmax, len - roff));
-	}
-
-	return rlen;
-}

libutf/utftorunestr.c

@@ -0,0 +1,13 @@
+/* See LICENSE file for copyright and license details. */
+#include "../utf.h"
+
+int
+utftorunestr(const char *str, Rune *r)
+{
+	int i, n;
+
+	for(i = 0; (n = chartorune(&r[i], str)) && r[i]; i++)
+		str += n;
+
+	return i;
+}