Overhaul `@Case` and `Cases` to `@Label` and `Labels`

[Pante]

This PR overhauls the existing @Case and Cases classes as discussed in #141. It contains several significant (breaking) changes to the API. Nevertheless, it should provide far superior ergonomics compared to the existing API.

Instead of deprecating and keeping @Case , a migration guide between Elementary 1.0.X to Elementary 2.0.X is provided.

[codecov[bot]]

Codecov Report

Base: 45.82% // Head: 46.00% // Increases project coverage by +0.18% :tada:

Coverage data is based on head (484b730) compared to base (71bd2db). Patch coverage: 82.05% of modified lines in pull request are covered.

Additional details and impacted files

@@             Coverage Diff              @@
##             master     #164      +/-   ##
============================================
+ Coverage     45.82%   46.00%   +0.18%     
+ Complexity      219      218       -1     
============================================
  Files            35       35              
  Lines          1017     1026       +9     
  Branches         97       99       +2     
============================================
+ Hits            466      472       +6     
- Misses          531      533       +2     
- Partials         20       21       +1     

Impacted Files	Coverage Δ
...in/java/com/karuslabs/elementary/junit/Labels.java	80.00% <80.00%> (ø)
...com/karuslabs/elementary/junit/DaemonCompiler.java	95.45% <100.00%> (ø)
...ain/java/com/karuslabs/elementary/junit/Tools.java	41.66% <100.00%> (ø)
...com/karuslabs/elementary/junit/ToolsExtension.java	85.71% <100.00%> (ø)

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