feat(webpack): add compression plugin

* Compresses `*.css`, `*.html`, `*.js` and `*.map` build assets
* Uses gzip with maximum compression level - 9

Closes linnovate#234

package.json

@@ -46,6 +46,7 @@
     "bluebird": "*",
     "blueimp-tmpl": "*",
     "colors": "^1.1.2",
+    "compression-webpack-plugin": "^0.2.0",
     "copy-webpack-plugin": "^0.3.3",
     "css-loader": "^0.23.0",
     "enhanced-resolve": "0.9.1",

webpack.prod.config.js

@@ -4,6 +4,7 @@
  * Helper: root(), and rootDir() are defined at the bottom
  */
 var path = require('path');
+var zlib = require('zlib');
 // Webpack Plugins
 var webpack = require('webpack');
 var ProvidePlugin = require('webpack/lib/ProvidePlugin');
@@ -12,6 +13,7 @@ var OccurenceOrderPlugin = require('webpack/lib/optimize/OccurenceOrderPlugin');
 var DedupePlugin = require('webpack/lib/optimize/DedupePlugin');
 var UglifyJsPlugin = require('webpack/lib/optimize/UglifyJsPlugin');
 var CommonsChunkPlugin = require('webpack/lib/optimize/CommonsChunkPlugin');
+var CompressionPlugin = require('compression-webpack-plugin');
 var CopyWebpackPlugin = require('copy-webpack-plugin');
 var HtmlWebpackPlugin = require('html-webpack-plugin');
 var WebpackMd5Hash    = require('webpack-md5-hash');
@@ -147,8 +149,13 @@ module.exports = {
       //mangle: {
       //  screw_ie8 : true
       //}
-    })
+    }),
    // include uglify in production
+    new CompressionPlugin({
+      algorithm: gzipMaxLevel,
+      regExp: /\.css$|\.html$|\.js$|\.map$/,
+      threshold: 2 * 1024
+    })
   ],
   // Other module loader config
   tslint: {
@@ -179,3 +186,7 @@ function rootNode(args) {
   args = Array.prototype.slice.call(arguments, 0);
   return root.apply(path, ['node_modules'].concat(args));
 }
+
+function gzipMaxLevel(buffer, callback) {
+  return zlib['gzip'](buffer, {level: 9}, callback)
+}