built year level index.html files

Added `bin/all-years.sh` to run a command over all years.

Added `bin/gen-year-index.sh` to build an `index.html`
for a given year.

Added support code to build an `index.html`
for a given year.

Added `make gen_year_index` to to level Makefile
and related rules.

Using the above, added `index.html` files for all IOCCC years.

Updated `bin/README.md` according to the above.

Improved comments in `bin/all-run.sh`.

Exported TOPDIR in all `bin/` tools that use TOPDIR.

Removed incorrect lines in `bin/quick-readme2index.sh`
usage message.

Improve -v 3 printed important variables messages,
in order that important variables are exported,
from all `bin/` tools.

Rebuild all HTML pages via `make www`.

bin/readme2index.sh

@@ -67,6 +67,7 @@ status="$?"
 if [[ $status -eq 0 ]]; then
     TOPDIR=$("$GIT_TOOL" rev-parse --show-toplevel)
 fi
+export TOPDIR
 export DOCROOT_SLASH="../../"
 export TAGLINE="bin/$NAME"
 export MD2HTML_SH="bin/md2html.sh"