Summary
Simplify specification of datasets in twines and manifests.
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Contents ([95](https://github.com/octue/twined/pull/95))
**IMPORTANT:** There are 2 breaking changes.
Enhancements
- **BREAKING CHANGE:** Require "datasets" field to be a dictionary in `manifest.json` files
- **BREAKING CHANGE:** Require "datasets" field in the "manifest" strands of `twine.json` to be a dictionary
- Raise error if JSON objects contain duplicate keys
Fixes
- Use correct method to transform manifests during validation
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