Add EvaluationTracker to docs and fix its docstring (#464)
* Fix definition of public in docstring
* Fix push_to_tensorboard param name in docstring
* Fix docstring style
* Add EvaluationTracker to docs
* Fix docstring style
* Move docstring to class header
* Add attributes to docstring
* Fix style
* Fix style
* Fix style
* Fix style
* Fix style
* Fix style
* Fix internal links in docstring
