Use delegating constructor for Integers

[mborland]

Also removes the bool constructors if they exists

Closes: #839

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.9%. Comparing base (cd1e650) to head (59fdb70).
Report is 8 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff            @@
##           develop    #852     +/-   ##
=========================================
- Coverage     98.9%   98.9%   -0.0%     
=========================================
  Files          231     231             
  Lines        17078   16755    -323     
  Branches      1809    1809             
=========================================
- Hits         16888   16563    -325     
- Misses         190     192      +2     

Files with missing lines	Coverage Δ
include/boost/decimal/decimal128.hpp	97.8% <100.0%> (-<0.1%)	⬇️
include/boost/decimal/decimal128_fast.hpp	98.4% <100.0%> (-<0.1%)	⬇️
include/boost/decimal/decimal32.hpp	98.6% <100.0%> (-<0.1%)	⬇️
include/boost/decimal/decimal32_fast.hpp	96.1% <100.0%> (-0.3%)	⬇️
include/boost/decimal/decimal64.hpp	99.0% <100.0%> (-<0.1%)	⬇️
include/boost/decimal/decimal64_fast.hpp	98.1% <100.0%> (-<0.1%)	⬇️

... and 32 files with indirect coverage changes

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