Notable changes:

• Batching has been reimplemented on top of the dedupe_seq.
• The "scan" phase has been reimplemented (see 8264336ea2a3b78e3bdce162fc389d02338af326 for details).
• Filesystem locking has been implemented. See f3947e9606f103417537974bc3dda4f6254c4503 for details.

This release focuses on improving the "scan" phase: restructure, remove bugs and improve its performance, as well as pave the way for future features. More bugs probably joined the party in the mean time, sadly.

Special thanks to Sergei Trofimovich for his kind insights, helps and contributions