Sends bytes through a socket to any other socket.
    The $QIO equivalent is the IO$_WRITEVBLK function.
    Format
      #include  <types.h>
      #include  <socket.h>
      int sendto  ( int s, char *msg, int len, int flags, struct
                  sockaddr *to, int tolen ); (_DECC_V4_SOURCE)
      ssize_t sendto  ( int s, const void *msg, size_t len, int
                      flags, const struct sockaddr *to, size_t tolen
                      ); (not_DECC_V4_SOURCE)