Split up is*rune() and to*rune() functions into individual source files

This optimizes the binary size for each tool that uses these functions.
Previously, if a program just used one single function, maybe even a
one-liner, it would statically compile in all lookup-tables, bloating
the binary by up to 20K.
All these changes are derived from a local libutf where I do the
primary changes. So I hope that I can merge these things into libutf
sooner or later, as discussed on the ml.

libutf/iscntrlrune.c

@@ -0,0 +1,19 @@
+/* Automatically generated by mkrunetype.awk */
+#include <stdlib.h>
+
+#include "../utf.h"
+#include "runetype.h"
+
+static Rune cntrl2[][2] = {
+	{ 0x0000, 0x001F },
+	{ 0x007F, 0x009F },
+};
+
+int
+iscntrlrune(Rune r)
+{
+	if(bsearch(&r, cntrl2, nelem(cntrl2), sizeof *cntrl2, &rune2cmp))
+		return 1;
+	return 0;
+}
+