message: Expose vega & vl, allow spec overwrites
diff: @@ -114,6 +114,11 @@ function embed(el, spec, opt, callback) {
  } catch (err) { cb(err); }
  + if (opt.onBeforeParse) {
  + // Allow Vega spec to be modified before being used
  + spec = opt.onBeforeParse(spec);
  + }
  +
  var runtime = vega.parse(spec, opt.config); // may throw an Error if parsing fails
  try {
  var view = new vega.View(runtime, opt.viewConfig)
  @@ -204,6 +209,10 @@ function viewSource(source) {
  // make config externally visible
  embed.config = config;
  +// expose vega and vegalite libs
  +embed.vega = vega;
  +embed.vegalite = vl;
  +
  // for es5
  module.exports = embed;
  // for es 6
  