Features:
- `dataset` module added
- Implements `SegmentationDataset` and `ClassificationDataset` which are PyTorch-formatted Dataset classes which allow for iteration of annotated structures in a set of slides. `SegmentationDataset` returns images and masks while `ClassificationDataset` returns images and labels (stored in GeoJSON properties). PyTorch installation is not required with this implementation, however, to integrate these datasets into a ML-pipeline one of the image/target/label transforms has to convert the data to a Tensor.