GNU R fast pseudo random number generators

 Several fast random number generators are provided as C++
 header only libraries: The PCG family by O'Neill (2014
 <https://www.cs.hmc.edu/tr/hmc-cs-2014-0905.pdf>) as well as
 Xoroshiro128+ and Xoshiro256+ by Blackman and Vigna (2018
 <arXiv:1805.01407>). In addition fast functions for generating random
 numbers according to a uniform, normal and exponential distribution
 are included. The latter two use the Ziggurat algorithm originally
 proposed by Marsaglia and Tsang (2000, <doi:10.18637/jss.v005.i08>).
 These functions are exported to R and as a C++ interface and are
 enabled for use with the default 64 bit generator from the PCG family,
 Xoroshiro128+ and Xoshiro256+ as well as the 64 bit version of the 20 rounds
 Threefry engine (Salmon et al., 2011 <doi:10.1145/2063384.2063405>) as
 provided by the package 'sitmo'.