* Add new SQUAD example

* Same with a task-specific Trainer

* Address review comment.

* Small fixes

* Initial work for XLNet

* Apply suggestions from code review

Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>

* Final clean up and working XLNet script

* Test and debug

* Final working version

* Add new SQUAD example

* Same with a task-specific Trainer

* Address review comment.

* Small fixes

* Initial work for XLNet

* Apply suggestions from code review

Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>

* Final clean up and working XLNet script

* Test and debug

* Final working version

* Add tick

* Update README

* Address review comments

Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>