author_lesson() to create swirl content

Note: This pull request does not affect existing codebase.

This solves the problem of how a potential course author gets started. However, we still need to figure out how to integrate a completed lesson/course...

1. Into the author's build of swirl, so they can test their newly created content
2. Into the central (swirldev) build of swirl, so the content can be shared with the world

I have ideas on both of these. We can discuss Wednesday.