Remove last references to .hint files

This changes in years.html the 2011/zucker/hint.html to
2011/zucker/README.md (at the top of the file - to do with the IOCCC
logo) and also 1998/dorssel/dorssel.hint to 1998/dorssel/dorssel.md in
years.html (which should have been done in
ccbbacb31b but was left out by accident).
As well it fixes 2004/gavin in bugs.md to refer to (in the Makefile rule
that is included) README.md.

There are still files with 'hint' in the name however. I believe these
to be correct.

bugs.md

@@ -1429,7 +1429,7 @@ gavin: gavin.c
         ${RM} -f vi
         ${CP} sh vi
         ${RM} -f fs.tar
-        ${TAR} -cvf fs.tar sh vi gavin.c gavin.hint prim
+        ${TAR} -cvf fs.tar sh vi gavin.c README.md prim
 
 gavin_clean:
         ${RM} -f sh vi kernel gavin.o