/// <summary>
 /// search commits
 /// https://developer.github.com/v3/search/#search-commits
 /// </summary>
 /// <param name="search"></param>
 /// <returns>List of commits</returns>
 public IObservable <SearchCommitsResult> SearchCommits(SearchCommitsRequest search)
 {
     Ensure.ArgumentNotNull(search, nameof(search));
     return(_client.SearchCommits(search).ToObservable());
 }