Changes in version 1.11:

A race has been fixed in zcmp and zdiff that sometimes made them return 1
(files differ) instead of 2 (trouble) when a compressor is not found or when
the wrong format is forced.

In case of error in an argument to a command line option, all tools now show
the name of the option.

In case of error in a numerical argument to a command line option, zcmp
now shows the name of the option and the range of valid values.

Support for the zstd format has been added to all tools. This allows, among
other things, zupdating zstd files to lzip format for long-term archiving,
and using zcmp along with the unzcrash tool (from the lziprecover package)
to test zstd files.

'zdiff --verbose --version' now prints the version of the diff program used
if it supports the option '--version'.

'zgrep --verbose --version' now prints the version of the grep program used
if it supports the option '--version'.

It has been documented in the manual how to recompress files with zupdate
from a read-only file system to another place by first linking the files
from the destination directory and then compressing the links:
'ln -s /src/foo.gz . && zupdate foo.gz'

The texinfo category of the manual has been changed from 'Data Compression'
to 'Compression' to match that of gzip. (Reported by Alfred M. Szmidt).
