A common use case is to iterate over more than one data set, and generate routes for all combinations between those sets. For example, if I am rendering a set of articles in a set of locales, it might look something like:

locales: ['en-US', 'de-DE', 'zh-TW']
articles: ['article-1', 'article-2', 'article-3']

/en-US
  /article-1
  /article-2
  /article-3
/zh-TW
  /article-1
  /article-2
  /article-3
/de-DE
  /article-1
  /article-2
  /article-3

At present, 11ty only indirectly supports this pattern. The burden of combining the data falls to the user, as described in #1412. This PR seeks to address that issue by adding full support for multiple pagination.

The API involves supplying pagination as an array of pagination objects. This allows us to cleanly support all existing pagination features with full backward compatibility. If a pagination array was supplied, the pagination in the data object will also be an array, with each pagination object in the array providing context specific to the corresponding data set. This allows for an extremely flexible user experience. Given the example above, I will have pagination context not only for neighboring articles in the same locale, but also neighboring localized versions of the same article.