Fix dead links in 2015/muth/machine_*.h

With the exception of those on the IOCCC website (maybe one other place
but don't think so) the links were dead. These have been replaced for
historical purposes with a captured copy on the Internet Wayback
Machine.

This entry should now be entirely complete.

2015/muth/machine_count_5_2.h

@@ -1,5 +1,5 @@
 /*
- * counting machine, http://www.drb.insel.de/~heiner/BB/mabu90.html
+ * counting machine, https://web.archive.org/web/20131104160623/http://www.drb.insel.de/~heiner/BB/mabu90.html
  *
  * does not halt
  */