Removed author tag inside channel tag in RSS

closes #2114
- instead of putting `author: user ? user.name : null` in feedOptions of node-rss, it was moved to itemOptions
- supplying `author: user ? user.name : null` in itemOptions will still result to creating a dc:creator tag inside item tags so the info needed to have the author is still there like before
- node-rss should still however fix it to not have that nasty author tag in channel tag when you supply author in feedOptions
- added a functional test