Improve comparison functions

[mborland]

Closes: #596
Closes: #591

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.1%. Comparing base (93d13a9) to head (dc2b4ac).
Report is 2 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff            @@
##           develop    #598     +/-   ##
=========================================
- Coverage     99.1%   99.1%   -0.0%     
=========================================
  Files          204     204             
  Lines        13343   13342      -1     
  Branches      1514    1511      -3     
=========================================
- Hits         13218   13217      -1     
  Misses         125     125             

Files	Coverage Δ
include/boost/decimal/decimal128.hpp	97.2% <100.0%> (-<0.1%)	⬇️
include/boost/decimal/decimal32.hpp	99.6% <100.0%> (-<0.1%)	⬇️
include/boost/decimal/decimal64.hpp	99.0% <100.0%> (-<0.1%)	⬇️
include/boost/decimal/detail/comparison.hpp	100.0% <100.0%> (ø)
...lude/boost/decimal/detail/integer_search_trees.hpp	100.0% <100.0%> (ø)

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 93d13a9...dc2b4ac. Read the comment docs.