h-feed to Atom conversion loses entry tags

[abhin4v]

My website provides an h-feed at https://abhinavsarkar.net/archive where each entry has tags in it tagged using class="p-category tag" rel="category tag". If I convert it to Atom using Granary I don't see the tags in the output. However, if I convert it to RSS, I do see the right tags.

[snarfed]

Thanks for filing @abhin4v! Great feature request, should be straightforward to add, it'd go into atom.from_as1, Atom category details in http://www.atomenabled.org/developers/syndication/#category . PRs are welcome!