correctly process non-zero EXIT_CODE, fix 2020/endoh2/README.md

We found cases where pandoc reported a conversion from markdown to
HTML problem that, while reported by the `bin/pandoc-wrapper.sh`
to `bin/md2html.sh`, which in turn reported to error to the tool
calling it, the tool calling `bin/md2html.sh` set `$EXIT_CODE` to
a non-zero value in order to delay the abort but then failed to act
on the non-zero `$EXIT_CODE` value at the end.

In a number of cases when `$EXIT_CODE` was set to non-zero, the
stderr message was labeled as a "Warning" instead of an "ERROR".

Fixed a bug in `bin/gen-authors.sh` that resulted the generation
of invalid markdown/HTML.  An `<hr>` HTML tag inside a `<div>` span
caused pandoc to issue "Div at .. closing implicitly" at the _hr_
HTML tag line.  For some reason, one cannot place a `<hr>`
(horizontal line) inside a `<div ... /div>` span.

Fixed a broken markdown links in `2020/endoh2/README.md` whose error
was hidden by one of the above mentioned problems.

Changed `bin/gen-authors.sh` VERSION from "1.10.1 2024-05-07"
to "1.10.2 2024-05-19" as a result of the above changes.

Changed `bin/gen-location.sh` VERSION from "1.4.1 2024-04-28"
to "1.4.2 2024-05-19" as a result of the above changes.

Changed `bin/gen-top-html.sh` VERSION from "1.4.6 2024-05-05"
to "1.4.5 2024-05-19" as a result of the above changes.

Changed `bin/gen-years.sh` VERSION from "1.3.1 2024-04-28"
to "1.3.2 2024-05-19" as a result of the above changes.

Changed `bin/quick-readme2index.sh` VERSION from "1.1.4 2024-04-13"
to "1.1.5 2024-05-19" as a result of the above changes.

Changed `bin/readme2index.sh` VERSION from "1.2.4 2024-04-14"
to "1.2.5 2024-05-19" as a result of the above changes.

Performed `make www` to test the above under macOS.

bin/quick-readme2index.sh

@@ -92,7 +92,7 @@ shopt -s globstar	# enable ** to match all files and zero or more directories an
 
 # set variables referenced in the usage message
 #
-export VERSION="1.1.4 2024-04-13"
+export VERSION="1.1.5 2024-05-19"
 NAME=$(basename "$0")
 export NAME
 export V_FLAG=0
@@ -549,7 +549,7 @@ if [[ -z $NOOP ]]; then
         "$README_PATH" "$INDEX_PATH"
     status="$?"
     if [[ $status -ne 0 ]]; then
-	echo "$0: Warning: md2html.sh: $MD2HTML_SH ${TOOL_OPTION[*]} -m $README_PATH --" \
+	echo "$0: ERROR: md2html.sh: $MD2HTML_SH ${TOOL_OPTION[*]} -m $README_PATH --" \
 	     "$README_PATH $INDEX_PATH failed, error: $status" 1>&2
 	EXIT_CODE="1"  # exit 1
 	echo "$0: Warning: EXIT_CODE set to: $EXIT_CODE" 1>&2
@@ -580,4 +580,7 @@ fi
 
 # All Done!!! -- Jessica Noll, Age 2
 #
-exit 0
+if [[ $EXIT_CODE -ne 0 ]]; then
+    echo "$0: Warning: about to exit $EXIT_CODE" 1>&2
+fi
+exit "$EXIT_CODE"