minor #1330 remove authors file and add more information to composer.json (Tobion)

This PR was merged into the 1.15-dev branch.

Discussion
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remove authors file and add more information to composer.json

I think the authors file is not needed. Also it was mentioned in the license file but it is not required to redistribute it, making it useless.
Also I updated the composer.json with more information and added the "Twig Team" as all contributors.

Commits
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3cc3813 remove authors file and add more information to composer.json