Add 512 bit xoshiro family

[mborland]

No description provided.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.49%. Comparing base (0690197) to head (2567f7f).
Report is 6 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #119      +/-   ##
===========================================
+ Coverage    95.25%   95.49%   +0.24%     
===========================================
  Files          106      109       +3     
  Lines         7122     7510     +388     
===========================================
+ Hits          6784     7172     +388     
  Misses         338      338              

Files with missing lines	Coverage Δ
include/boost/random/detail/xoshiro_base.hpp	100.00% <100.00%> (ø)
include/boost/random/xoshiro.hpp	100.00% <100.00%> (ø)
test/test_comp_xoshiro512d.cpp	100.00% <100.00%> (ø)
test/test_comp_xoshiro512mm.cpp	100.00% <100.00%> (ø)
test/test_comp_xoshiro512pp.cpp	100.00% <100.00%> (ø)

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