* Remove manually-added bold style for titles in [User guide] section
* Fix failed relative links in windows user guide
* Remove manually-added bold style for titles in [Orca] section
* Fix failed relative links & title bold fix in Nano 5 min
* Remove manually-added bold style for titles in [Nano] section
* Remove manually-added bold style for titles in [DLlib] section
* Remove manually-added bold style for titles in [Chronos] section
* Remove manually-added bold style for titles in Developer guide
* Remove manually-added bold title style for all other not-included md files in docs/readthedocs/source/doc folder
* Fix based on comments
* rename backend name from tf2 to ray
* rename in doc
* rename in docstring
* manually
* rename test_tf2estimator_tf2_backend.py -> test_tf2estimator_ray_backend.py
* change tf2 in multi_agent_two_trainers.py back