The pack command packs the given snap-dir as a snap and writes the result to
target-dir. If target-dir is omitted, the result is written to current
directory. If both source-dir and target-dir are omitted, the pack command packs
the current directory.
The default file name for a snap can be derived entirely from its snap.yaml, but
in some situations it's simpler for a script to feed the filename in. In those
cases, --filename can be given to override the default. If this filename is
not absolute it will be taken as relative to target-dir.
When used with --check-skeleton, pack only checks whether snap-dir contains
valid snap metadata and raises an error otherwise. Application commands listed
in snap metadata file, but appearing with incorrect permission bits result in an
error. Commands that are missing from snap-dir are listed in diagnostic
messages.
