Abstraction of a special value representing an struct.
An opaque type representation used to model struct type defined inside the XML-RPC standard.
To create a struct the following function is used:
Then new struct members are added using:
Once the struct is no longer needed, a call to vortex_xml_rpc_struct_free could be done.
Remember that this is not required if the struct is added to a method value (XmlRpcMethodValue).