idea: extend luajit's ffi.cdef so that it can return introspection information

cdef-sample.lua

-- Something like (ZeroMQ in this case)

return {
   typedefs = {
      functions = {
         zmq_free_fn = { "void", "data", "hint" },
      },
      structs = {
         zmq_pollitem_t = "zmq_pollitem_t"
      },
   },
   functions = {
      zmq_version = { [0]="", "int*", "int*", "int*" }
      zmq_errno = { "int" }
   }
   unions = {

   },
   structs = {
      zmq_msg_t = {

      },
   },
   enums = {
      ZMQ_VERSION_MAJOR = 2,
   },
}

-- The table above would be returned by ffi.cdef() if asked for it (could be ffi.cdefx, as in extended info)