Fix #9: RDoc::Markup::Paragraph objects have no 'each' method.

Instead, they have a 'parts' method that returns
an enumerator. This patch uses that enumerator to walk
through the authors and append them to the authors
hash.
Merge pull request #10 from diranged/issue-9

Fix #9: RDoc::Markup::Paragraph objects have no 'each' method.