Feature request: checksum progress

[ulmemxpoc]

When using zsync with large files (for example, ISO files containing an operating system), the progress of checksums is only *************************. There is no indication how much longer it will take for the checksums. zsync is not particularly useful for small files (little bandwidth saved), so checksum progress for large files will be useful.

zsync \
  -i LARGE_FILE \
  -o LOCAL_LARGE_FILE \
  http://example.com/LARGER_FILE.zsync