Defining a New Stream
   The following steps are required to define a new stream in C:
     
- Define low level functions (character reading, writing etc).
     
 - Initialize and open your stream.
     
 - Allocate memory needed for your particular stream.
     
 - Initialize and install a Prolog stream with
SP_make_stream() or SP_make_stream_context().
      - Initialize additional fields.  Some streams may require additional
changes to the fields in the 
SP_stream structure than the default
values set by SP_make_stream().