Style analysis for examples

[thomascorthals]

I've added the examples dir to .styleci.yml, fixed the errors StyleCI reported, and then applied the same fixes to the code examples in docs. (I don't think StyleCI can analyse the codeblocks inside Markdown.)

The most visible part will be that we no longer use array(...) but [...] as we already did in the codebase. Feels more modern IMHO. Besides that the bulk of the changes is removing whitespace around the concatenation operator ..

Also added a few manual improvements, e.g. using $client->select() instead of $client->execute() because it plays nicer with an IDE's autocomplete.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.21%. Comparing base (b0f6a64) to head (65ce23f).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1172   +/-   ##
=======================================
  Coverage   98.21%   98.21%           
=======================================
  Files         404      404           
  Lines       10647    10647           
=======================================
  Hits        10457    10457           
  Misses        190      190           

Flag	Coverage Δ
unittests	98.21% <ø> (ø)

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