Memoize some functions, and fix up some parts that were not randomizing

Signed-off-by: Ken Barber <ken@bob.sh>
No need to pass metadata to parse-tar-entry

Signed-off-by: Ken Barber <ken@bob.sh>
Use pmap where necessary and treat some metaparameters specially

Signed-off-by: Ken Barber <ken@bob.sh>