Fix/3 log grouping

[kjczarne]

List all Issues this Pull Request is meant to solve:

• [x] Closes #3

Run through our contribution checklist:

• [x] Have you read kalash/doc/contributing.md?
• [x] Have you added tests for the implemented feature/fixed bug?
• [x] Have you ran a full test suite (nox -e test)?
• [x] Have you checked if the test coverage is at least 85%? -> (#4 still open)
• [x] Have you ran code style check (flake8)?
• [x] Have you documented the change?
• [x] Have you updated CHANGELOG.md?

Describe shortly the changes you have introduced: Now logs are group-able by any metadata tags.

Add additional comments (if any): N/A

[codecov-commenter]

Codecov Report

Merging #12 (a4c62de) into develop (c8b0a6b) will increase coverage by 0.37%. The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop      #12      +/-   ##
===========================================
+ Coverage    76.14%   76.52%   +0.37%     
===========================================
  Files           14       14              
  Lines          805      818      +13     
===========================================
+ Hits           613      626      +13     
  Misses         192      192              

Impacted Files	Coverage Δ
kalash/collectors.py	91.42% <ø> (ø)
kalash/log.py	93.82% <100.00%> (+1.07%)	:arrow_up:
kalash/test_case.py	73.52% <100.00%> (+0.80%)	:arrow_up:

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