code: func Run(generators ...generator) {
  	for _, generator := range generators {
  		dslengine.PrintFilesOrFail(generator.Generate())
  	}
  }
docs: // Run runs all generators passed as parameter. Call ParseDSL first to
  // fill `design.Design`.  Each `goa` generator lives in its own
  // `goagen/gen_something` package in `generator.go` and has a
  // `Generator` object which implements the interface required here.
  //
  //   codegen.Run(
  //     &genapp.Generator{
  //       API: design.Design,
  //       Target: "app",
  //     },
  //     &genmain.Generator{
  //       API: design.Design,
  //     },
  //   )
  //