Automatically remove empty releases or releases which are released in the future, regardless of the product.
Also refactored a bit releasedata.py to use better names and clarify types.
Copy releases, without their properties, from product data (frontmatter) to release data.
This script is not intended to be declared in the frontmatter: it is for internal use only.
It executes before all other scripts, and helps the following scripts to work with releases.