Added an independent script to generate folder-based collections.json outside of a kindle.
epub_metadata now passes flake8. Minor class changes for metadata.
A few more steps to unify the interface for db metadata and ebook metadata.
Fixed when openlibrary search gives no result. Everything in librarianlib now passes flake8.
Added new option -a to list all authors in the library.
librarian now passes flake8 without warnings.