examples: Add many new examples and improve existing ones

[stotko]

Since the first release of the library, there were only very few updates to the examples which mostly consisted of minor warning fixes. Since they are crucial for beginners and interested users to get to know stdgpu, we should put more attention to it. Add many new examples for atomic, bitset, deque, unordered_map, unordered_set, and vector and improve the existing ones.

Supersedes #13

[codecov]

Codecov Report

Merging #173 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #173   +/-   ##
=======================================
  Coverage   97.80%   97.80%           
=======================================
  Files          28       28           
  Lines        1825     1825           
=======================================
  Hits         1785     1785           
  Misses         40       40           

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