The RepositoryContent struct doesn't quite map to the API because it is
missing a download link.  This link is very useful because while the API
doesn't allow large files to be downloaded, the link allows the raw
files to be downloaded outside the API.

The issue is that the JSON tags on the contents struct were wrong.  They
were missing the underscore.

With this code it should be possible to tick the ‘Content’ box in issue
#37. The code is written after reviewing PR #64 and so is (very)
loosely based on that PR. So big thanks for the work already done by
@octavore! I did however had some different insights about a few fixes
and as the PR hasn’t moved for the last 5 months, I thought to just
rewrite and PR and I send in a new PR hoping to come to a merge…