Use Util.filename_to_utf8 to Books.path
Implemtn 'honyomi edit -t'
Add Help message
See ENV['HONYOMI_DATABASE_DIR'] in Core#db_dir
Public Core#db_dir, di_path
Show error message when the database does not exist
Change init help message
Add TestCli#test_init
Merge branch 'feature/improve-init'
Don't raise error when execute 'honyomi list' on empty database