Add support for associative arrays

Hi,

In my work I needed to pass assoc arrays as parameters to stored-procedures so I've added this option to node-oracle.
I am using setDataBufferArray of occi and not SetVector because the latter doesn't support assoc arrays that are defined in Packages (SetVector should get the assoc array type name).

The last time I did C++ was > 10 years ago so my code might have issues, anyone care to review ??
Thx.