improve topbar

The icons used to show the menu open (`png/hamburger-icon-open.png`)
and closed (`png/hamburger-icon-closed.png`) have been added.

Changed `inc/topbar.default.html` to use the png icons instead
of a svg file.

A new page `nojs-menu.html` has been added for when
JavaScript is disabled.

Changed `bin/gen-top-html.sh` VERSION from to "1.4.4 2024-04-21"
to "1.4.5 2024-04-23".

Sorted top sections in `inc/md2html.cfg` and added
a section for `nojs-menu.md`.

Fixed `ioccc.css` so that the topbar and related pulldown
menus had the correct background colour.

Ran `make www` to perform the above.

TODO: Detect when JavaScript is disabled and display:

		Please
		Enable
	      JavaScript

      As a link to the new `nojs-menu.html` page.

TODO: Fix a problem on wide screens where some of
      the righthand edge pulldown menus are cutoff.

TODO: Fix the 5 HTML 5 errors introduced by the topbar code.

bin/gen-top-html.sh

@@ -87,7 +87,7 @@ shopt -s globstar	# enable ** to match all files and zero or more directories an
 
 # set variables referenced in the usage message
 #
-export VERSION="1.4.4 2024-04-21"
+export VERSION="1.4.5 2024-04-23"
 NAME=$(basename "$0")
 export NAME
 export V_FLAG=0
@@ -126,8 +126,9 @@ TOP_MD_SET+=("license")
 TOP_MD_SET+=("markdown")
 TOP_MD_SET+=("news")
 TOP_MD_SET+=("next/README")
-TOP_MD_SET+=("next/rules")
 TOP_MD_SET+=("next/guidelines")
+TOP_MD_SET+=("next/rules")
+TOP_MD_SET+=("nojs-menu")
 TOP_MD_SET+=("thanks-for-help")
 #
 export NOOP=