Add support for array-of-struct

[PeterJohnson]

Right now we have support for array-of-native and raw data types. The latter can easily be used to create an array of structured data but there's currently no standard way of doing this. A standardized format for array-of-struct would enable viewers and users to have a common way to communicate more complex data in an atomic fashion. It could be as simple as prepending a string of data types (ala Python's struct module) to the raw data elements, as you can derive the element size from the string of data types and the array size from the raw data length divided by the element size.