Features
- Added the [Datasets](https://kevinmusgrave.github.io/pytorch-metric-learning/datasets) module for easy downloading of common datasets:
- [CUB200](https://kevinmusgrave.github.io/pytorch-metric-learning/datasets/#cub-200-2011)
- [Cars196](https://kevinmusgrave.github.io/pytorch-metric-learning/datasets/#cars196)
- [INaturalist 2018](https://kevinmusgrave.github.io/pytorch-metric-learning/datasets/#inaturalist2018)
- [Stanford Online Products](https://kevinmusgrave.github.io/pytorch-metric-learning/datasets/#stanfordonlineproducts)
Thanks ir2718!