Update NEWS.md with these changes and slack deltas for empty file sigs.
Update NEWS.md with these changes and slack deltas for empty file sigs.

sourcefrog/librsync,dbaarda/librsync,librsync/librsync,librsync/librsync,sourcefrog/librsync,dbaarda/librsync,librsync/librsync,librsync/librsync,sourcefrog/librsync,sourcefrog/librsync,dbaarda/librsync,dbaarda/librsync