[doc] improve documentation of make targets and ./manage script

BTW force modularization of the ./mange script into sub modules:

- utils/lib_sxng_data.sh
- utils/lib_sxng_node.sh
- utils/lib_sxng_static.sh
- utils/lib_sxng_test.sh
- utils/lib_sxng_themes.sh

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

utils/lib_sxng_themes.sh

@@ -0,0 +1,65 @@
+#!/usr/bin/env bash
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
+declare _Blue
+declare _creset
+
+themes.help(){
+    cat <<EOF
+themes.:
+  all       : build all themes
+  live      : to get live builds of CSS & JS use 'LIVE_THEME=simple make run'
+  simple.:
+    build   : build simple theme
+    test    : test simple theme
+EOF
+}
+
+themes.all() {
+    (   set -e
+        pygments.less
+        node.env
+        themes.simple
+    )
+    dump_return $?
+}
+
+themes.live() {
+    local LIVE_THEME="${LIVE_THEME:-${1}}"
+    case "${LIVE_THEME}" in
+        simple)
+            theme="searx/static/themes/${LIVE_THEME}"
+            ;;
+        '')
+            die_caller 42 "missing theme argument"
+            ;;
+        *)
+            die_caller 42 "unknown theme '${LIVE_THEME}' // [simple]'"
+            ;;
+    esac
+    build_msg GRUNT "theme: $1 (live build)"
+    nodejs.ensure
+    cd "${theme}"
+    {
+        npm install
+        npm run watch
+    } 2>&1 \
+        | prefix_stdout "${_Blue}THEME ${1} ${_creset}  " \
+        | grep -E --ignore-case --color 'error[s]?[:]? |warning[s]?[:]? |'
+}
+
+themes.simple() {
+    (   set -e
+        build_msg GRUNT "theme: simple"
+        npm --prefix searx/static/themes/simple run build
+    )
+    dump_return $?
+}
+
+themes.simple.test() {
+    build_msg TEST "theme: simple"
+    nodejs.ensure
+    npm --prefix searx/static/themes/simple install
+    npm --prefix searx/static/themes/simple run test
+    dump_return $?
+}