Merge tag '2.1.1' into develop

2.1.1

This is a bug fix release for ExhibitBuilder 3 integration. See #14.
Tweaked release checklist.
Changed the rendered API to return DOMDocuments.
Set @alt and @title in Fedora items' ExhibitBuilder output.

This is so jQuery ColorBox will find the captions.

Refs #14.
Merge branch 'feature/lightbox-caption' into develop
Set version number to 2.1.2.
Merge branch 'release/2.1.2'