Fix boost min/max guidelines violations

[mborland]

Closes: #251

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.85%. Comparing base (25dfbce) to head (e52759e).
Report is 2 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #254   +/-   ##
========================================
  Coverage    94.85%   94.85%           
========================================
  Files           69       69           
  Lines         9077     9077           
========================================
  Hits          8610     8610           
  Misses         467      467           

Files with missing lines	Coverage Δ
include/boost/charconv/detail/emulated128.hpp	100.00% <ø> (ø)
...nclude/boost/charconv/detail/fallback_routines.hpp	84.61% <ø> (ø)
.../boost/charconv/detail/fast_float/parse_number.hpp	92.18% <ø> (ø)
src/from_chars_float_impl.hpp	82.97% <ø> (ø)
test/from_chars.cpp	100.00% <100.00%> (ø)
test/limits.cpp	100.00% <100.00%> (ø)
test/roundtrip.cpp	98.75% <100.00%> (ø)
test/test_128bit_emulation.cpp	100.00% <100.00%> (ø)
test/test_128bit_native.cpp	100.00% <100.00%> (ø)
test/test_parser.cpp	100.00% <100.00%> (ø)
... and 2 more

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