code: function drizzle(options) {
    return init(options)
      .then(prepare)
      .then(parse)
      .then(render)
      .then(write);
  }
docs: Build the drizzle! This will:
  - Init: Parse and merge passed options with defaults
  - Prepare templating—partials, templates, helpers
  - Parse files—data, patterns, pages, layouts—and organize a data object
  - Render templates, collections, pages
  - Write rendered data to the filesystem
  
  @param {Object} options   User options for the build
  @return {Promise} resolving to {Object} of all data generated and used