remove SliceBuilder and Transaction

[Herringway]

Let this mess trouble us no more.

[codecov]

Codecov Report

Merging #315 (beedc90) into master (2c915b3) will decrease coverage by 0.07%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #315      +/-   ##
==========================================
- Coverage   95.20%   95.13%   -0.07%     
==========================================
  Files          29       29              
  Lines        4569     4505      -64     
==========================================
- Hits         4350     4286      -64     
  Misses        219      219              

Files Changed	Coverage Δ
source/dyaml/reader.d	98.47% <ø> (-0.37%)	⬇️
source/dyaml/scanner.d	99.65% <100.00%> (-0.01%)	⬇️

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