Added examples of using non-scalar data with dynamodb

issue #76 

I realized that there is a slight breaking change with how AttributeValue is coerced: Previously a vector was coerced to a number-set or string-set, but now clojure vectors are coerced to lists. I think this is reasonable as number-sets and string-sets are marshalled as clojure sets. That is, to represent a number-set or string-set you should use a clojure set. 

Hopefully this documentation explains how to use the non-scalar types.