Whiiif v2.0.0

This version brings the new approach of using a Solr plugin to provide more accurate and controllable search results.

Major changes:

• The solr-ocrhighlighting plugin from the MDZ Digital Library team at the Bavarian State Library is now the engine behind Whiiif.
• Two new endpoints to complement the IIIF Search functionality
  • Collections Search a.k.a Search Across - Retrieve contextualised snippets from all documents in the Whiiif index
  • Snippets Search - Retrieve contextualised snippets for a single document
• Unit tests!