* Add callback system + associated test
* Add trainer and pl_module args to callback methods
* typing
* typo in docstring
* Switch to on_.*_start()
* fix on_test_start
* fix the mess after rebasing
* added outline of all features
* updated common use cases doc
* updated common use cases doc
* updated common use cases doc
* updated common use cases doc
* updated common use cases doc
* updated common use cases doc
* updated common use cases doc
* updated common use cases doc
* updated common use cases doc
* updated common use cases doc
* updated common use cases doc
* updated common use cases doc
* updated common use cases doc
* updated docs