SearchWP 4.4.0

[Note]** Rebuilding your index using the Rebuild Index button on the Engines tab of the SearchWP settings screen is recommended after updating
[Fix]** Delta update regression introduced in `4.0.13`
[Fix]** Error when applying delta update to Source that no longer exists
[Improvement]** Handling of delta update process during failures
[Improvement]** Delta update queue handling during index rebuild

[Fix]** Issue where partial matches from keyword stems were not found in some cases
[Fix]** Partial match token processing limited to applicable site(s)
[Fix]** Excerpt generation when handling unregistered Shortcodes

[Fix]** Loss of tokens when applying partial match logic in some cases
[Update]** Revised MySQL minimum to 5.6 because of `utf8mb4_unicode_520_ci` collation requirement