Switch build to use browserify (#502)

package.json

@@ -2,7 +2,7 @@
   "title": "html2canvas",
   "name": "html2canvas",
   "description": "Screenshots with JavaScript",
-  "main": "main.js",
+  "main": "src/core.js",
   "version": "0.5.0-alpha1",
   "author": {
     "name": "Niklas von Hertzen",
@@ -12,7 +12,9 @@
   "engines": {
     "node": ">=0.10.0"
   },
-  "dependencies": {},
+  "dependencies": {
+    "es6-promise": "^2.0.1"
+  },
   "repository": {
     "type": "git",
     "url": "git@github.com:niklasvh/html2canvas.git"
@@ -25,7 +27,7 @@
     "bluebird": "^2.7.1",
     "bower": "^1.3.12",
     "grunt": "^0.4.5",
-    "grunt-contrib-concat": "^0.5.0",
+    "grunt-browserify": "^3.3.0",
     "grunt-contrib-connect": "^0.8.0",
     "grunt-contrib-jshint": "^0.10.0",
     "grunt-contrib-uglify": "^0.6.0",