Add bitwise operators to decimal128

[mborland]

Closes: #321

[codecov]

Codecov Report

Merging #327 (d5b4054) into develop (0907caf) will increase coverage by 0.1%.
The diff coverage is 100.0%.

Additional details and impacted files

@@            Coverage Diff            @@
##           develop    #327     +/-   ##
=========================================
+ Coverage     97.3%   97.3%   +0.1%     
=========================================
  Files           71      71             
  Lines         3230    3243     +13     
=========================================
+ Hits          3140    3153     +13     
  Misses          90      90             

Files	Coverage Δ
include/boost/decimal/decimal128.hpp	93.1% <100.0%> (+0.3%)	⬆️

... and 1 file with indirect coverage changes

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