Package: Explicitly list files to include when publishing

The entry in .gitignore tells npm to also ignore the dist/ folder,
adding it to files overrides that. It also excludes everything else,
so we add some more useful files explicitly.

Fixes #223
Closes gh-224

package.json

@@ -11,6 +11,7 @@
     "type": "git",
     "url": "git://github.com/jquery/PEP.git"
   },
+  "files": ["dist/", "src/", "pointerevents.js", "samples/"],
   "bugs": "https://github.com/jquery/PEP/issues",
   "license": "MIT",
   "devDependencies": {