Lpd

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* Added predict method to trainer
* Added State.PREDICT enum
* Added Phase.PREDICT_BEGIN and Phase.PREDICT_END enums
* Added CollectOutputs callback
* Added predict example
* Moving some elements from nn.functional to nn
* Added sample count to save/load model

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* Fix in Tensorboard metrics output

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* Added Phase and States validations to Callbacks
* Added callbacks summary to trainer's summary
* Added to trainer optimizer_step_and_zero_grad_criteria
* Added sample_count and sample_count_in_epoch to Trainer and CallbackContext
* StatsPrint will now print sample count
* Added accumulate grads example
* Changed cuda.manual_seed to cuda.manual_seed_all

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* bug fix in StatsPrint - print round numbers

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* Added KerasDecay scheduler
* Added KerasDecay usage example
* Better printing in StatsPrint callback when using multiple metrics

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* Fixed bug in TrainerStats for dynamic batch size
* Added support for metric name as string in StatsPrint callback
* Fixed some descriptions
* Updated README