improve .gitignore files, fix index.html links, sync CNAME

fix experimental web site links in experimental index.html

sync CNAME with https://github.com/ioccc-src/winner/blob/master/CNAME

improve .gitignore files

Added to each .gitignore file, comments on how to sort.

Put into winner .gitignore files, ignore *.dSYM files.

Put into winner .gitignore files, ignore indent.c,
indent.o and indent files.  This is done so that the
winner directory can more self contained.

We did not put into winner .gitignore files, however,
excludes of .-files as found in the top level .gitignore file.
As .-files are not allowed by mkiocccentry, the top level
.gitignore file remains sufficient.

Added to year level .gitignore files, excludes of
mkentry or iocccsize files as needed.

Sorted (via sort -d -u) all .gitignore file.

2020/.gitignore

@@ -1,18 +1,4 @@
-burton/check
-burton/check_be
-burton/prog_be
-endoh2/spoiler/
-endoh3/clock
-endoh3/clock.c
-endoh3/run_clock
-ferguson2/recode
-kurdyukov2/out.gif
-kurdyukov2/out*.jpg
-kurdyukov2/output.ppm
-kurdyukov2/random.ppm
-kurdyukov2/prog_png
-kurdyukov2/prog_ppm
-kurdyukov3/prog.extra
-kurdyukov3/prog.orig
-yang/code.c
-yang/encoded.c
+#
+# sort with: sort -d -u
+iocccsize
+iocccsize.o