machinary to demonstrate ccall with types-as-structs
implement ccall-with-types-as-structs interface
add sizeof(::CompositeKind) for the sizeof the a struct
ccall struct return types
add proper errors for invalid ccall struct types
add support for unsafe_ref for a struct type
add emitted cpointer check, fix tests
fix ccalls in stream and socket
Merge pull request #1831 from vtjnash/jn/ccall_struct

RFC: ccall with julia types as structs