code: function init(config) {
      if (!config) config = getConfigFromPackageJSON();
      if (!config.version || !config.publicKeys || !config.manifests) {
          throw new Error('Malformed updater config');
      }
      return new Updater(config);
  }
docs: /*
  
  config = {
  version: "1.0.0",
  publicKeys: [
  "xxx...",
  "yyy..."
  ],
  manifests: [
  "github:bla/bla"
  "https://example.com/manifest.txt"
  ]
  }
  
  or in package.json
  
  {
  ...
  "version": "1.0.0", // as usual
  "updater": {
  publicKeys: ...,
  manifests: ...
  }
  }
  
   
  Initializes updater and returns it.
  
  @typedef {Object} Config
  @property {string} version current semver version (1.0.0)
  @property {Array<string>} publicKeys public keys for manifest verification
  @property {Array<string>} manifests manifest URLs as described above
  @property {boolean} nightly if true, uses a different "nightly" installer for Mac