code: func migrate(args []string, r *githistory.Rewriter, l *tasklog.Logger, opts *githistory.RewriteOptions) {
  	requireInRepo()
  
  	opts, err := rewriteOptions(args, opts, l)
  	if err != nil {
  		ExitWithError(err)
  	}
  
  	_, err = r.Rewrite(opts)
  	if err != nil {
  		ExitWithError(err)
  	}
  }
docs: // migrate takes the given command and arguments, *gitobj.ObjectDatabase, as well
  // as a BlobRewriteFn to apply, and performs a migration.