Adding new configuration parameter: document.cover.always_convert which by default is set to "false". If true - no matter what output type is specified cover will always be prepared for Kindle (same ways as it is done by default for mobi and azw3 formats). Using "send to Kindle" functionality (--stk) automatically sets always_convert to true.
Switching to go1.20.1 and updating all dependencies to address some minor bugs in used libraries.