Threefry2x32

[hikettei]

• Implement threefry2x32 proposed in https://www.thesalmons.org/john/random123/papers/random123sc11.pdf
• Implement !rand
• Implement the SoTA beta sampling algorithm (the same as cl-waffe2) https://github.com/hikettei/cl-waffe2/blob/master/source/distributions/dense.lisp
• as well as chisquare, gamma distribution
• randn (Ziggurat) https://github.com/hikettei/cl-waffe2/blob/master/source/distributions/ziggurat.lisp
• xavier-uniform https://github.com/hikettei/cl-waffe2/blob/master/source/distributions/weights.lisp
• non-lazy distribution initializer at external/distribution/beta.lisp, ziggurat.lisp, etc ...
• Xavier/He/orthogonal

Changes

• Fix a bug existing in purge-isolated-graph (recursive if the graph is a cyclic)
• Fix ci for ccl-bin (using ccl-bin/1.12.0)
• Added :wrap-around option for %add %mul
  • TODO: wrap-around should be an expected behaviour on the all devices; add tests
  • Fix: _rng_counter
• Added %xor