Fix / improve dynamodbv2 value data type support:

* Accept any number (not just integers)
* Return longs or doubles from gets, as necessitated by values'
  string representation
* Add support for binary and binary set values (byte[] or ByteBuffer
  values are accepted; ByteBuffers are returned per the AWS SDK)
Be more polite w/ dynamodbv2 set return values

* Marshall string set and byte-array set values to Clojure sets
* Don't marshall Clojure sets into vectors
Merge pull request #16 from cemerick/master

Fix / improve dynamodbv2 value data type support