[RFC] - Arrays

I'm slowly working on arrays.  I don't expect this to be done any time soon.  

I think that it will take time and research into a number of backends to find the right abstractions here, particularly for broadcasting, elementwise operations, and tensor contractions (dot products.)  

Nothing on this PR is particularly adventurous or opinionated.  None of the hard stuff is here.

Still, it might be nice to have something concrete on which to play.