fix: use idiomatic go style for write channels

[andig]

Closes #145

• make signalling channels of type struct

• use closing of signalling channels instead of sending messages

• CHANGELOG.md updated

• Rebased/mergeable

• Tests pass

• Sign CLA (if not already signed)

[codecov-commenter]

Codecov Report

Merging #154 into master will decrease coverage by 0.08%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #154      +/-   ##
==========================================
- Coverage   79.20%   79.12%   -0.09%     
==========================================
  Files          26       26              
  Lines        1784     1777       -7     
==========================================
- Hits         1413     1406       -7     
  Misses        245      245              
  Partials      126      126              

Impacted Files	Coverage Δ
api/write.go	93.75% <100.00%> (-0.37%)	⬇️

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[vlastahajek]

Thanks for the PR!