Simplify non-finite number functions and handling

[mborland]

Closes: #697

[codecov]

Codecov Report

Attention: Patch coverage is 95.89041% with 3 lines in your changes missing coverage. Please review.

Project coverage is 99.2%. Comparing base (ae81dea) to head (55bfdeb).

Additional details and impacted files

@@            Coverage Diff            @@
##           develop    #699     +/-   ##
=========================================
+ Coverage     99.1%   99.2%   +0.1%     
=========================================
  Files          230     230             
  Lines        16307   16290     -17     
  Branches      1742    1757     +15     
=========================================
- Hits         16160   16146     -14     
+ Misses         147     144      -3     

Files	Coverage Δ
include/boost/decimal/decimal128.hpp	98.1% <100.0%> (+0.3%)	⬆️
include/boost/decimal/decimal128_fast.hpp	97.5% <100.0%> (+1.3%)	⬆️
include/boost/decimal/decimal32.hpp	99.8% <100.0%> (-<0.1%)	⬇️
include/boost/decimal/decimal64.hpp	99.3% <100.0%> (-<0.1%)	⬇️
include/boost/decimal/decimal32_fast.hpp	97.1% <91.0%> (-<0.1%)	⬇️
include/boost/decimal/decimal64_fast.hpp	98.6% <91.0%> (-<0.1%)	⬇️
include/boost/decimal/detail/cmath/fpclassify.hpp	87.5% <66.7%> (-2.5%)	⬇️

... and 6 files with indirect coverage changes

---

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 ae81dea...55bfdeb. Read the comment docs.