mannixsuo

Support Multiple Row Merge

3

 `mergeCells` command is not easy to use if I need merge many rows , like the picture show, I want merge many rows in single command or less command...

/session endpoint was removed in GitLab 10.2+ so i add oauth2 login method ```java GitlabAPI api = GitlabAPI.oauth2Login("http://localhost", "username", "password"); ```