feat: support multiple links in AtomFeeds struct

[phirework]

The Atom spec allows multiple links in the Feed object, and this is required for support of things like PubSubHubbub.

Also closes #111 I believe because you can just add your own link rel="self" entry.

What type of PR is this? (check all applicable)

• [ ] Refactor
• [x] Feature
• [ ] Bug Fix
• [ ] Optimization
• [ ] Documentation Update
• [ ] Go Version Update
• [ ] Dependency Update

Description

Related Tickets & Documents

• Related Issue #
• Closes #

Added/updated tests?

• [x] Yes
• [ ] No, and this is why: please replace this line with details on why tests have not been included
• [ ] I need help with writing tests

Run verifications and test

• [x] make verify is passing
• [x] make test is passing