Accept processor functions by API call

[danielalves]

We could add another configuration key, by API call, with a function to process the request response:

var manifest = {
  host: 'http://my.api.com',
  resources: {
    Book: {
      all:  { 
        path: '/v1/books.json', 
        processor: function( data ){ // i.e: data contains 'results', 'pagination', ...
          return data.results;
        } 
      }
    }
  }
}