
Map: negative indices interpreted as from end.

Physical copying & write back?

The resulting objects are HUGE! At the moment there is debugging
info there but even barring that, there is too much.
Need to make some of PDL::PP just call functions to do the job
to avoid bloat.

Also, need to make the strings more generic in the "%s %d" format
to have less copying.

Variable numbers of arguments.

Flexible numbers of output dimensions for a variable - growing
on the fly.
