Update versions in pom.xml and documentation after 0.2.0 release

[github-actions]

• Versions are updated in pom.xml, README.md and in examples
• Current project version is incremented to the next snapshot

[codecov]

Codecov Report

Merging #674 (426dc51) into master (e2df0c8) will increase coverage by 0.84%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master     #674      +/-   ##
============================================
+ Coverage     79.05%   79.90%   +0.84%     
  Complexity     1816     1816              
============================================
  Files            87       87              
  Lines          4732     4732              
  Branches       1525     1525              
============================================
+ Hits           3741     3781      +40     
+ Misses          285      239      -46     
- Partials        706      712       +6     

Flag	Coverage Δ	Complexity Δ
unittests	79.90% <ø> (+0.84%)	0.00 <ø> (ø)

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Impacted Files	Coverage Δ	Complexity Δ
...lin/org/cqfn/diktat/plugin/maven/DiktatBaseMojo.kt	78.94% <0.00%> (+57.89%)	0.00% <0.00%> (ø%)
.../kotlin/org/cqfn/diktat/plugin/maven/DiktatMojo.kt	80.00% <0.00%> (+70.00%)	0.00% <0.00%> (ø%)

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