* Add a few LR schedulers
* Move parents's constructor call to the top
* Fix docstring
* refactor optimizers into two files
* add docs
* nit
* Fix Callable type annotation for python 3.8
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Co-authored-by: Awni Hannun <awni@apple.com>
Co-authored-by: Angelos Katharopoulos <a_katharopoulos@apple.com>
