Added two more examples
Added two more examples

Add an example of two structs in, and a struct return (#'complex-add)
and a struct and a non-struct in, and a struct return
(#'complex-add-real), illustrating the need to pass every argument by
reference, including the :double.

dkochmanski/cffi,mcna/cffi,stassats/cffi,stassats/cffi,dkochmanski/cffi,attila-lendvai/cffi,mcna/cffi,attila-lendvai/cffi,stassats/cffi,3b/cffi,cffi/cffi,3b/cffi,3b/cffi,dkochmanski/cffi,cffi/cffi,cffi/cffi