Handle and Organise Posts by Different Authors and Contributors

[sirinath]

This relates to #959 and #955.

If multiple authors are contributing to a blog then:

• one should have a collection of posts and metadata about the author as a collection to generate
  • list of authors by
    • 1st letter of the name
    • topics written / areas covered - using taxonomies
  • author bio pages - no post templates / sections
  • list of posts by authors

[zachleat]

Cross-link to #4051