add offline enabled build process

gulpfile.js

@@ -0,0 +1,37 @@
+
+var gulp = require('gulp');
+// var uglify = require('gulp-uglify');
+// var minifyCSS = require('gulp-csso');
+var useref = require('gulp-useref');
+
+gulp.task('css', function(){
+  return gulp.src([
+    'src/lib/codemirror/lib/codemirror.css',
+    'src/lib/codemirror/addon/hint/show-hint.css',
+     'src/lib/codemirror/addon/fold/foldgutter.css',
+     'src/lib/hint.min.css',
+     'src/lib/inlet.css',
+     'src/style.css',
+   ])
+    .pipe(concat('build.css'))
+    .pipe(minifyCSS())
+    .pipe(gulp.dest('src'))
+});
+
+gulp.task('useRef', [],function() {
+  return gulp.src('src/index.html')
+      .pipe(useref())
+      .pipe(gulp.dest('dist'));
+});
+
+gulp.task('generate-service-worker', [ 'useRef' ], function(callback) {
+  var swPrecache = require('sw-precache');
+  var rootDir = 'dist';
+
+  swPrecache.write(`${rootDir}/service-worker.js`, {
+    staticFileGlobs: [rootDir + '/**/*.{js,html,css,png,jpg,gif,svg,eot,ttf,woff}'],
+    stripPrefix: rootDir
+  }, callback);
+});
+
+gulp.task('default', [ 'generate-service-worker' ]);