Add 32-bit FMA implementation

[mborland]

Introduces a proper FMA and also a template that allows for us to skip all the non-finite checks as suggested by @ckormanyos

Closes: #769

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.7%. Comparing base (b9adb39) to head (30c0fba).
Report is 24 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff            @@
##           develop    #770     +/-   ##
=========================================
- Coverage     98.7%   98.7%   -0.0%     
=========================================
  Files          223     223             
  Lines        16728   16742     +14     
  Branches      1796    1798      +2     
=========================================
+ Hits         16503   16516     +13     
- Misses         225     226      +1     

Files with missing lines	Coverage Δ
include/boost/decimal/decimal32.hpp	98.6% <ø> (ø)
include/boost/decimal/decimal32_fast.hpp	96.5% <ø> (-0.3%)	⬇️
include/boost/decimal/detail/cmath/fma.hpp	100.0% <100.0%> (ø)
include/boost/decimal/detail/mul_impl.hpp	93.6% <ø> (-0.5%)	⬇️
include/boost/decimal/literals.hpp	100.0% <100.0%> (ø)
test/test_big_uints.cpp	100.0% <ø> (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 b9adb39...30c0fba. Read the comment docs.