Ldct-benchmark

**Main changes:**

- Add the winning entry (team agaldran) of the *Low-dose Computed Tomography Perceptual Image Quality Assessment Grand Challenge 2023* as a no-reference perceptual image quality assessment metric for low-dose CT images (https://github.com/eeulig/ldct-benchmark/pull/4)
- Add hyperparameter optimization via W&B's sweeps (https://github.com/eeulig/ldct-benchmark/pull/8)


**Full Changelog**: https://github.com/eeulig/ldct-benchmark/compare/0.0.7...0.0.15

**Changelog:**

- Fixed a bug in the script to download the LDCT data that caused the script to crash.
- Use the [NCI Imaging Data Commons](https://portal.imaging.datacommons.cancer.gov/explore/filters/?collection_id=nlm_visible_human_project) hosted version of the Visible Human Project CT data for testing and the introductory example.
- Fixed some typos in the documentation and code.