GitLab

* increase atol for Half-Float comparison to 1.5e-4

* disable tests for different opt_levels

* reset atol

* add bitwise accurate comparison

* add state_dict, load_state_dict

* add test_restoring, test_loss_scale_decrease

* disable amp outputs for checkpoint tests

* add test for amp.state_dict, cleanup

* add state_dict patch, add test

* fixed testing, cleanup

* add readme for checkpointing

* add docs to source/amp

* add review changes to doc