support only pandoc for markdown rendering

dropped support for other renderers, simplifies code and make results
consistent. using markdown_github flavor with html5 target

render

@@ -302,36 +302,28 @@ render_html() {
 
     # first pass marks the markdown parts and saves them separate
     mds=(`find . -name 'tmp.md*'`)
-    { test "${#mds}" = "0" } || {
+    [[ "${#mds}" = "0" ]] || {
         # second pass substituted saved parts with rendered markdown
         act -n "${#mds} markdown fields "
 
         # check which markdown parser is available in PATH
-        command -v pandoc > /dev/null
-        if [[ $? = 0 ]]; then parser="pandoc -f markdown_github -t html5"
-        else command -v maruku > /dev/null
-             if [[ $? = 0 ]]; then parser="maruku --html-frag"
-             else command -v markdown > /dev/null;
-                  if [[ $? = 0 ]]; then parser=markdown
-                  else command -v multimarkdown > /dev/null
-                       if [[ $? = 0 ]]; then parser=multimarkdown
-                       else
-                           error "no markdown renderer installed, please install pandoc or equivalent"
-                           return 1
-                       fi
-                  fi
-             fi
-        fi
+        if command -v pandoc > /dev/null; then
+			parser="pandoc -f markdown_github -t html5"
 
-        # parses all html and renders each markdown in the html
-        for i in $mds; do
-            md=`basename $i`
-            newtemp="tmp.$RANDOM"
-            cat $tmp | awk '
+			# parses all html and renders each markdown in the html
+			for i in $mds; do
+				md=`basename $i`
+				newtemp="tmp.$RANDOM"
+				cat $tmp | awk '
 /^'"$md"'/ { system("cat '"$md"' | '"$parser"'"); next }
 { print $0; }' > $newtemp
-            rm $tmp; tmp=$newtemp
-        done
+				rm $tmp; tmp=$newtemp
+			done
+
+		else
+			error "Required program not found: pandoc"
+			error "Install pandoc on this system to render markdown"
+		fi
     }
 
     cat $tmp