Return leading image for {{content words="0"}}

Closes #3884
- This PR includes a reimplementation of Downsize@0.0.5 with `words: "0"`. It uses the same parsing methods, therefore guarunteeing identical behavior.
- Tests have been updated to be more extensive.
Merge pull request #3888 from felixrieseberg/iss3884-content

Return leading image for {{content words="0"}}