Associative primer

This PR adds a primer for associative domains and arrays. It is intended to demonstrate features exclusive to associative domains and arrays. 
I'd add an assignment to Scores here as well, just to round this out (make "Mark" look like he's now a full-fledged person).  This would also emphasize the fact that we have two arrays tracking Mark.

Quibbly: I might also make his age >18 just because 18 feels like such a baggage-laden age.