[Feature Request] Please add an option to mobitool and user can extract .mobi or .azw3 only.

[jack6th]

Currently mobitool -t can output both .mobi and .azw3.
If the user has thousands of mobi files and he only want .azw3 files, generating all the .mobi and .azw3 and then delete all .mobi is waste of time and disk space. Please add an option like -k8 or -k7 to the mobitool and the user can extract only one type of them.