We rename `bin/gen-top-md2html.sh` to `bin/gen-top-html.sh`.
Modified the `bin/gen-top-html.sh` tool to build `archive/historic/index.html`
from `archive/historic/README.md`.
In `bin/gen-top-html.sh` changed VERSION from "1.1 2024-02-28"
to "1.2 2024-02-29".
Renamed `make gen_top_md2html` to `gen_top_html` in the top level `Makefile`.
Improved `archive/historic/README.md`.
Updated `robots.txt` to include the Sitemap directive.
Moved unused `valid-html401.png` to `png/valid-html401.png`.
This png image may be used later.
Performed `make gen_top_html` which rebuilt all top level HTML files
as well as `bin/index.html` and `inc/index.html`.
Landon Curt Noll
fb43b1dfef
