Zip refactoring

[Orace]

This PR continues #639 since I erroneously deleted it's branch.

[Orace]

To improve the documentation, we may get a lesson from System.Linq.Enumerable.Zip method.

[codecov[bot]]

Codecov Report

Merging #715 (d514db0) into master (aefa90b) will decrease coverage by 2.03%. The diff coverage is 60.63%.

:exclamation: Current head d514db0 differs from pull request most recent head c49ee41. Consider uploading reports for the commit c49ee41 to get more accurate results

@@            Coverage Diff             @@
##           master     #715      +/-   ##
==========================================
- Coverage   92.49%   90.47%   -2.03%     
==========================================
  Files         113      113              
  Lines        3424     3506      +82     
  Branches     1024     1055      +31     
==========================================
+ Hits         3167     3172       +5     
- Misses        192      265      +73     
- Partials       65       69       +4     

Impacted Files	Coverage Δ
MoreLinq/ZipLongest.g.cs	49.42% <49.42%> (ø)
MoreLinq/ZipShortest.g.cs	54.16% <54.16%> (ø)
MoreLinq/EquiZip.g.cs	70.83% <70.83%> (ø)
MoreLinq/Enumerator.cs	100.00% <100.00%> (ø)

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