Standardise on `\'` instead of `&#8217;` for default article

There were already instances of `\’` and `&#8217;`. The excerpt was
populated with `&#8217;` not encoded. This PR chooses `\’` instead of
`&#8217;` and replaces 7 instances.
Merge pull request #454 from petecooper/master

Standardise on `\'` instead of `&#8217;` for default article apostrophes