Maybe allow broadcasting across ragged-sized entities

[mohawk2]

It might be of interest to allow this (see https://en.wikipedia.org/wiki/Jagged_array) generally, since non-rectangular data can be a "thing". Also it might simplify PDL::Graphics::PLplot since that now uses Iliffe vectors internally with its plAlloc2dGrid et al. That would mean loop() would need to be aware, and $SIZE(n) would vary.

There would need to be some additional structure to store the length of each sub-entry, since the point of this is to allow that to vary (though it wouldn't for the rectangular data used by PLplot).