Add base experiments for common tasks

[rosikand]

i.e., create sample experiments for classification, segmentation, etc. (low priority and just a maybe)

[rosikand]

Add this to 'experiment.py'

[rosikand]

Also make 'datasets.py' which defines common datasets to use such as XYDataset, Episodic classification dataset, classificationdatasetfromfolder, episodic xy dataset, meta batch sampler, etc.

Also make 'algorithms.py' which implements new algorithms such as MAML, protoner, DDPM, etc.