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/runetype.c

@@ -1,4 +1,5 @@
 /* MIT/X Consortium Copyright (c) 2012 Connor Lane Smith <cls@lubutu.com>
+ *                            (c) 2015 Laslo Hunhold <dev@frign.de>
  *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the "Software"),
@@ -18,16 +19,8 @@
  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
  * DEALINGS IN THE SOFTWARE.
  */
-#include <stdlib.h>
 #include "../utf.h"
 
-#define nelem(x)  (sizeof (x) / sizeof *(x))
-
-static int rune1cmp(const void *, const void *);
-static int rune2cmp(const void *, const void *);
-
-#include "../runetypebody.h"
-
 int
 rune1cmp(const void *v1, const void *v2)
 {