Fill in missing stuff from case_study schema
Expand on case study example to include links
Add related_policies/worldwide priorities to schema

These are the last two remaining bits of meta data required for a complete case
study representation.
Merge pull request #1 from alphagov/fill-out-case-study-format

Fill out case study format
Merge pull request #2 from alphagov/add-fields-to-case-study-format

Add remaining meta data to case study format
Rename 'backend' to 'publisher' schema

This reflects the naming conventions just agreed in [1].

[1]
https://gov-uk.atlassian.net/wiki/display/WH/RFC2%3A+naming+content+format+representations
Update readme to reflect naming conventions