Random Number Generator

Since YAP-4.3.19 YAP uses the O'Keefe public-domain algorithm, based on the "Applied Statistics" algorithm AS183.

The following random number operations are included with the use_module(library(random)) command.

In ROK's words: `This is algorithm AS 183 from Applied Statistics. I also have a C version. It is really very good. It is straightforward to make a version which yields 15-bit random integers using only integer arithmetic.'