Parametrize expand_variables

Add flexiblility for more specialized targets

src/include/build.sh

     dstpath=$2
     test -n "$dstpath" || dstpath=${srcpath%.skel}
     case $dstpath in
-        *.md) <"$srcpath" expand_includes | expand_variables >"$dstpath" ;;
-        *)    <"$srcpath"                   expand_variables >"$dstpath" ;;
+        *.md) <"$srcpath" expand_includes | expand_variables "vars" >"$dstpath" ;;
+        *)    <"$srcpath"                   expand_variables "vars" >"$dstpath" ;;
     esac
     mkdir -p "$MKIT_LOCAL"
     echo "$dstpath" >> "$MKIT_LOCAL/built.lst"
 
 expand_variables() {
     #
-    # Expand variable values
+    # Expand variables from sections $@
     #
     local script=$(mktemp --tmpdir mkit-tmp.XXXXXXXXXX)
-    local varname varvalue
-    ini lskeys "vars" \
-      | while read varname;
-        do
-            varvalue="$(ini 1value "vars:$varname" | sed -e 's/\$/\\$/' )"
-            echo "s|$varname|$varvalue|;" >> "$script"
-        done
+    local section varname varvalue
+    for section in "$@";
+    do
+        ini lskeys "$section" \
+          | while read varname;
+            do
+                varvalue="$(ini 1value "$section:$varname" | sed -e 's/\$/\\$/' )"
+                echo "s|$varname|$varvalue|;" >> "$script"
+            done
+    done
     echo "s|__CODENAME__|$CODENAME|;"     >> "$script"
     echo "s|__VERSION__|$(get_version)|;" >> "$script"
     perl -wp "$script" || die "expand_variables failed"