Threadmarks Pro 2.21.1

• Fix "SV\Threadmarks\Job\Cache::getNextIds(): Return value must be of type array, null returned" error generated when installing add-on.
  This did not block the installer or cause the add-on to fail, but could cause repeated errors if the site was in debug mode.
• Fix edge case with installer when the add-on is deleted and re-installed when extended by other add-ons

• Fix not syncing the threadmark state when the post state changes (ie deleted)

• Fix various numerical admincp options which did not step in the incremental values as intended, while allowing arbitrary values in the range to be entered

• Fix approval queue could have lingering non-visible threadmarks waiting for approval
• Fix soft-deleting a moderated thread with a moderated threadmark on the first post would leave an entry in the approval queue
• Fix non-active threadmark index could be picked using "Content with threadmark index url" option when posting a new thread

• Require Standard Library by Xon v1.18.0+
• Implement XF2.2 LinkableInterface interface for various entities where it makes sense
• Change 'threadmark-index-icon' to silently return an empty string is passed null for the threadmark index, and allow the href parameter to work without being in update mode
• Add "Use threadmark index icon instead of avatar" per-forum option (default: false)

• Fix unknown template macro error on creating a new thread when a threadmark index is required but a user isn't permitted to create one
• Add 'backdate' option when adding a threadmark
  • Sets the threadmark create date to the content's, and sets the threadmark creator to the thread/conversation starter

• Fix template error when next/previous threadmark's content has been hard-deleted but not the threadmark metadata

• Require php 7.2+
• If installed, require Search Improvements v2.6.0+
• Support Search Improvements v2.7.0+ search term display
• Compatibility fix for @NixFifty's Discord integration add-on
• Compatibility fix for Collaborative Threads add-on
• Fix threadmark author statistics column alignment
• Fix missing phrases
• Fix 'xf-rebuild:missing-threadmark-index' on threads with threadmarks and missing the first post

• Only show threadmark index status filter on forums a user can view threadmark indexes in

• Improve php 8.2 compatibility
• Fix 'Search title only' would get deselected when going from a search to the search-form via the clickable link