Full support of age encryption

mktar-batch now supports non-interactive age calls, though I've added a
dependency on expect.

tarcat, tarls, and untar now know what to do with .age files. They also
now know what to do with Zstandard compressed files that use .zstd
(instead of .zst).

Big archival update

mktar now experimentally supports SHA256 checksums and age encryption.

mktar-batch is a version of mktar that strips out the 'clever' algorithm
detection and includes a batch processing/common passphrase mechanism.

Updated tests for mktar.