Current code will create an archive in the current directory with:
% archive ../test.tar.gz test.*
or will complain that the following archive doesn't exist in the current
directory (given it actually exists in the parent one):
% unarchive ../test.tar.gz
Fix that and allow archives in any directory.
Other changes:
* Use `<required_param>` instead of `[required_param]` in the usage text
* Don't explictly check if archive exists in `unarchive`, but let the
respective tool fail with its own message
Closes#312
2e3ba7996b