The stream_out_t chain creation is modified: all modules are created by
the core (or by stream_out_duplicate) instead of being created by the
previous module.
sout_StreamChain{New,Delete} replace sout_Stream{New,Delete} to handle
modules chains instead of individual modules
sout_Stream{New,Delete} are still used by those new functions but made
static inside stream_output.c
Remove now unneeded psz_chain from struct sout_instance_t
Replace pointer to chain of next module by pointer to next module in
struct sout_stream_t