Fix building of markdown files

Code include expansion overwrote result of variable name expansion.

(This had no effect so far since there are no variables in markdown
files.)

setup/mk.sh

@@ -36,11 +36,15 @@ build1() {
     local srcpath dstpath
     srcpath=$1
     dstpath=${srcpath%.skel}
-    expand_variables < $srcpath > $dstpath
-    if grep -qe '.md$' <<<"$dstpath";
-    then
-        expand_includes < $srcpath > $dstpath
-    fi
+    case $dstpath in
+        *.md)   cat $srcpath \
+                  | expand_includes \
+                  | expand_variables \
+                > $dstpath ;;
+        *)      cat $srcpath \
+                  | expand_variables \
+                > $dstpath ;;
+    esac
     echo $dstpath >> built.list
 }