Fix thread-loader memory leaks and worker and main process lifecycles

[mistic]

This PR is very important and should be merged and released as a patch as soon as possible.
It basically fixes a memory leak introduced by #42 and also fixes the lifecycle both for the worker and for the main process from thread-loader. With those changes we should be able to get away with every issue related with getting the thread-loader hanging or outputting broken pipe errors directly into the shell stdout after running.

The tests were also updated.

CC\ @evilebottnawi

[codecov]

Codecov Report

Merging #51 into master will decrease coverage by 0.27%.
The diff coverage is 13.63%.

@@            Coverage Diff             @@
##           master      #51      +/-   ##
==========================================
- Coverage   17.26%   16.98%   -0.28%     
==========================================
  Files           7        7              
  Lines         365      424      +59     
  Branches       60       71      +11     
==========================================
+ Hits           63       72       +9     
- Misses        268      309      +41     
- Partials       34       43       +9

Impacted Files	Coverage Δ
src/readBuffer.js	37.5% <0%> (+4.16%)	⬆️
src/worker.js	0% <0%> (ø)	⬆️
src/WorkerPool.js	23.38% <31.57%> (+2.42%)	⬆️

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[alexander-akait]

Good work, will be great increase coverage to 80-90%, but we can do it in other PRs