examples,src,test: Fix readability-magic-numbers warnings

[stotko]

In addition the recent warning fixes (see #140), there are still some warnings left. Fix these readability-magic-numbers warnings to ensure clean builds under clang-tidy-8.

[codecov]

Codecov Report

Merging #141 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #141   +/-   ##
=======================================
  Coverage   97.64%   97.64%           
=======================================
  Files          28       28           
  Lines        1698     1698           
=======================================
  Hits         1658     1658           
  Misses         40       40           

Impacted Files	Coverage Δ
src/stdgpu/impl/limits_detail.h	100.00% <100.00%> (ø)

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