Adding support for libruks

Added new inpx format (output) "--inpx-format=ruks". Resulting inpx will contain one extra field (md5 from database - if avaialble, issue #3 )

Starting from 03/17/2017 flibusta stopped exporting lib.libavtoraliase.sql.gz - handle this gracefully (with warning) rather than fail. It is quite possible that this table does not have useful information anymore (result comparison for fb2 books shows only 2 meaningful differences).