Use Ironclad and Babel-Streams instead of md5sum and sha1sum.
Drop external-program-word, not needed anymore.
Use NAMESTRING rather than PRINC-TO-STRING.
Ensure that simple-vector type is given to Ironclad

Or else it fails. What comes out of babel-streams is an adjustable
array with a fill pointer.
make location of GNU tar configurable
Merge pull request #3 from valeryz/simple-vector

Ensure that simple-vector type is given to Ironclad
Merge pull request #4 from valeryz/master

Make location of GNU Tar configurable via *gnutar*.
Update documentation.  Add metainfo.  Set licence to Unlicense.