Document changed interface of sprng

Description: Use Debian packaged libsprng

Author: Andreas Tille <tille@debian.org>

Last-Update: Mon, 08 Jul 2019 16:47:12 +0200

  ATTENTION: Please double check the change in src/util.c.

             The Debian packaged sprng seems to have a different

             interface for init_sprng (quoting from CHANGES.TEXT):

                               Changes in Version 2.0

                  ----------------------

        Using the previous version of SPRNG, a user can use only one of the

        SPRNG generators in one run of the program. The objective of the new

        version is to combine the current random number generators (RNGs) into

        a single library so that a user can use all of them in a single program

        at a same time.

        The user now is able to and needs to specify the type of RNG when a

        random number stream is initialized. We add one integer argument

        rng_type to the front of the argument list of the function init_sprng.

        int *init_sprng(int rng_type, 

                int stream_number, int nstreams, int seed, int rng_parameter) 

           SPRNG_POINTER init_sprng(integer rng_type,

                           integer streamnum, integer nstreams,

                           integer seed, integer param)

        User can sprcify one of the follows for rng_type:

         SPRNG_LFG 

         SPRNG_LCG 

         SPRNG_LCG64 

         SPRNG_CMRG 

         SPRNG_MLFG 

         SPRNG_PMLCG 

        The following macros are added to sprng.h and sprng_f.h:

        #define SPRNG_LFG       0

        #define SPRNG_LCG       1

        #define SPRNG_LCG64 2

        #define SPRNG_CMRG      3

        #define SPRNG_MLFG      4

        #define SPRNG_PMLCG 5

        For simple interface, a user can only have one random number stream at

        one time since he doesn't specify stream ID.  

        The default generator is "SPRNG_LFG".

        User still can change RNG at runtime by calling init_sprng:

        int *init_sprng(int rng_type, 

                int seed, int rng_parameter) 

           SPRNG_POINTER init_sprng(integer rng_type,

                           integer seed, integer param)

--- a/src/Makefile.am

+++ b/src/Makefile.am