address #93

address #92

add BYOLTrainer for huggingface accelerate distributed training

concat augmented images and only call online encoder once

remove some inplace operations

just automatically sync batchnorm if more than one machine detected, …

…allow for overriding with sync_batchnorm keyword argument

fix simsiam, thanks to @chingisooinar

add more informative error message

default to returning projections, but can be turned off with return_p…

…rojection = False on forward