Support Nested Structs

[fubuloubu]

As of #1115, structs with basic type members are added as args to functions. With more complex use cases it may be necessary to nest a struct within a struct, and therefore it would be useful to allow our function argument parsing and return parsing to accept nested structs as arguments.

This was split out from #1019 as a complicated edge case deserving of it's own issue to track progress.

[charles-cooper]

closed as of #2447