rename bin/gen-top-html.sh, added archive/historic/index.html

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`.

inc/index.html

@@ -10,7 +10,7 @@
 <!-- -->
 <!-- END: this line ends content from: inc/top.default.html -->
 <!-- -->
-<!-- The original markdown content was formed by the tool: bin/gen-top-md2html.sh -->
+<!-- The original markdown content was formed by the tool: bin/gen-top-html.sh -->
 <!-- The HTML was converted from markdown by the tool: bin/md2html.sh -->
 <!-- -->
 <!-- START: this line starts content from: inc/head.default.html -->

inc/md2html.cfg

@@ -259,6 +259,22 @@ years.md
 	-D
 	./
 
+archive/historic/README.md
+	-H
+	topnav=.
+	-o
+	bin/subst.default.sh
+	-s
+	TITLE=The International Obfuscated C Code Contest
+	-s
+	DESCRIPTION=Historic archive of IOCCC winning entries
+	-s
+	KEYWORDS=IOCCC, archive, historic, historic archive, IOCCC archive
+	-s
+	HEADER_2=Historic archive of IOCCC winning entries
+	-D
+	../../
+
 bin/README.md
 	-H
 	topnav=.