Release notes

Enhancements

• Added new shutdown method to async encoders to more easily ensure the end
  of output is written and I/O cleaned up. Previously this required a call to
  .get_mut().shutdown().await
• Changed AsyncDynWriter and AsyncDbnEncoder::with_zstd to use a zstd checksum like
  the sync equivalents
• Added new publisher values for XNAS.BASIC and XNAS.NLS

Bug fixes

• Fixed bug where DBN metadata would still be upgraded after passing AsIs to
  DbnDecoder::set_upgrade_policy and AsyncDbnDecoder::set_upgrade_policy