Don't ignore "hoodie.hoodiejs" setting

This adds (or reintroduces) support for the `hoodie.hoodiejs` setting specified in `package.json`.

The one thing to note is that when using a custom `hoodie.js` you should point `hoodie.hoodiejs` to `hoodie.js` in the `src` directory instead of `dist`. This is because browserify dynamically builds the bundle. So `package.json` could look something like:

```json
{
  ...
  "hoodie": {
    "plugins": [
      "hoodie-plugin-appconfig",
      "hoodie-plugin-email",
      "hoodie-plugin-users"
    ],
    "hoodiejs": "node_modules/hoodie/src/hoodie.js"
  ...
}
```

This should close #247