Integration with 3rd party full text engines

Made it possible to integrate with 3rd party full text engines like Lunr 2, Minisearch, and other.

What's Changed

• Update link to CMU DIG website by @domoritz in #68
• Handle items internally with _id and not id by @cigolpl in #70
• Custom fulltext by @cigolpl in #72
• hot fix and lint fix by @cigolpl in #73

New Contributors

• @domoritz made their first contribution in #68

Full Changelog: v2.0.1...v2.1.1