Calibre 9.2.1 introduces Mustache templating and key security fixes

Calibre 9.2.1 switches ZIP output HTML templating from templite to Mustache, resulting in a breaking change for custom templates. This release fixes path traversal vulnerabilities in CHM and EPUB input files and viewer and bookshelf issues. Additional improvements include a new option to rebuild the annotations search index and disabling template based searches in the Content server for unauthenticated users.