update year level .filelist

Added new YYYY/index.html files.

Removed var.mk as such special top level files are
added (or not) in various bin tools.

2020/.filelist

@@ -6,9 +6,9 @@
 2020/.gitignore
 2020/guidelines.txt
 2020/hint.css
+2020/index.html
 2020/iocccsize.c
 2020/iocccsize.mk
 2020/iocccsize-test.sh
 2020/rules.txt
 2020/.year
-var.mk