Incorporate various dataset splits

[jasperhyp]

I also have one suggestion for future updates of this library perhaps. The current dataloaders, if I'm not mistaken, are not considering the different dataset split strategies. Recent works have highlighted the importance of evaluations on different dataset splits, e.g. split pairs, split drugs, split cell lines (for synergy), etc. It would be great to see this library also having such features.

[cthoyt]

Would be happy to review a PR if you want to submit one