[sbml-arrays] Infix syntax for arrays

[Lucian S. <luc...@gm...>]

So, we've had a couple different discussions about infix syntax for arrays,
but it's all been hypothetical up until now.  At this point, after Sarah's
heroic efforts getting extended MathML into libSBML's 'ASTNode' system, I
am actually in a position to implement infix support for it!  So we need to
make some final decisions.

I've written up a document of what all I think we need to decide at:

https://docs.google.com/document/d/1z9QLbmfltAIOkPcR883g4Ml5S7B5crJULXMX68ImL6k/edit#

Feel free to comment, edit, and whatever else!

-Lucian