Package usrmerge: Information

- 0.5 -> 0.6; see commit history for details.
  Notably:
  + Made hier-convert to call fsync(2) just after the conversion.

- 0.4 -> 0.5; see commit history for details.
  Notably:
  + Taught hier-convert to fix symlinks in unmerged dirs pointing
    to a location which usrmerge maps to itself. (Closes: 49472)
- Introduced new subpackages:
  + usrmerge-block;
  + usrmerge-ensure.

- 0.3 -> 0.4; see commit history for details.
  Notably:
  + Added a resolution rule for byte-for-byte equivalent symlinks.
    (Closes: 49533)