Change repository structure to include per tutorial code example.

[larxn]

Hi, I'm trying to do this changes:

• Include a per tutorial code example branch.
• Update Django and DRF versions.

The first one requires you to create the following branches, so I can pull request to them:

• 2-requests-and-responses
• 3-class-based-views
• 4-authentication-and-permissions
• 5-relationships-and-hyperlinked-apis
• 6-viewsets-and-routers
• 7-schemas-and-client-libraries
• heroku-example

Note that the first tutorial is gonna live on master. For the complete preview of this changes, please check my fork. Thank you.

[rpkilby]

Closing per #47