Add PreChunk and PreVacant

[tkf]

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[codecov]

Codecov Report

Merging #464 (ddeedb6) into master (eb6f73a) will decrease coverage by 0.03%.
The diff coverage is 89.65%.

@@            Coverage Diff             @@
##           master     #464      +/-   ##
==========================================
- Coverage   91.41%   91.37%   -0.04%     
==========================================
  Files          32       32              
  Lines        2120     2157      +37     
==========================================
+ Hits         1938     1971      +33     
- Misses        182      186       +4     

Flag	Coverage Δ
unittests	91.37% <89.65%> (-0.04%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/splitby.jl	94.06% <89.65%> (-2.23%)	⬇️

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