VSCode warnings

[damianodegaspari]

What I did.

• Changed a bunch of iterations from for i in 1:length(vec) to for i in eachindex(vec);
• I substituted a loop with a list comprehension because it seemed faster and clearer to read;
• Changed some iterations from for i in 1:length(vec) to for item in vec;
• I correct some spelling typos in comments in the code;
• I replaced comparisons of the type a == nothing with isnothing(a).

I run the tests locally and there were no problems.

Why I did it.

• In the process of figuring out the correct formatting in my latest pull request on documentation, I cloned the repository locally and did the changes with VSCode. VSCode was giving about 50 warnings. Those changes bring them down to 15. The ones left are mostly Possible method call error, which I don't really know how to fix;
• I wanted to practice with git, github and contribution to open source projects in general.

They are very small changes and definitely not very important. I hope they are welcome anyway. If not (for example because reviewing them would take away time from the maintainer which would be better spent otherwise) do not hesitate to let me know, so that I won't do similar pull requests in the future.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.31%. Comparing base (12ac6ba) to head (8b59571).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #423   +/-   ##
=======================================
  Coverage   97.31%   97.31%           
=======================================
  Files         117      117           
  Lines        6956     6956           
=======================================
  Hits         6769     6769           
  Misses        187      187           

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