SHA512/256

[mborland]

Implements SHA512/256 and makes a simplification to all of the classes. Rather than inheriting into an empty class the hashers are now a simple Alisas from a using = statement. This avoids a hasher being 3 levels of classes.

Closes: #52
Closes: #25

[cppalliance-bot]

An automated preview of the documentation is available at https://53.crypt.prtest2.cppalliance.org/libs/crypt/doc/html/index.html

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (0296d5a) to head (cf78ef4).
Report is 13 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff             @@
##           develop       #53    +/-   ##
==========================================
  Coverage   100.00%   100.00%            
==========================================
  Files           36        40     +4     
  Lines         1890      2083   +193     
  Branches       220       241    +21     
==========================================
+ Hits          1890      2083   +193     

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