Further simplifications to builder pattern

[spookylukey]

This builds on #216 as per the comments there.

[faif]

@spookylukey Fails to build. Can you please fix it? :)

[codecov-io]

Codecov Report

Merging #223 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #223      +/-   ##
==========================================
+ Coverage   97.02%   97.03%   +<.01%     
==========================================
  Files          61       61              
  Lines        2288     2294       +6     
==========================================
+ Hits         2220     2226       +6     
  Misses         68       68

Impacted Files	Coverage Δ
tests/test_builder.py	100% <100%> (ø)	⬆️
creational/builder.py	95.12% <100%> (+0.67%)	⬆️
structural/decorator.py	100% <0%> (ø)	⬆️

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