add "npm run build" command for producing standalone build

package.json

@@ -9,13 +9,16 @@
   },
   "main": "lib/b64.js",
   "scripts": {
+    "build": "browserify -s base64js -r ./ | uglifyjs -m > base64js.min.js",
     "test": "standard && tape test/*.js"
   },
   "license": "MIT",
   "dependencies": {},
   "devDependencies": {
     "benchmark": "^2.1.0",
+    "browserify": "^13.0.0",
     "standard": "^6.0.5",
-    "tape": "4.x"
+    "tape": "4.x",
+    "uglify-js": "^2.6.2"
   }
 }