Many updates

[Paebbels]

• Bump version to v1.1.5 and file headers to 2021.
• Change test runner to pytest.
• Rework GHA workflow files.
• Use @export from pydecor to register classes in __all__.
• Add dependencies in documentation
• Update setup.py
• Update conf.py

[codecov]

Codecov Report

Merging #2 (5220c90) into master (6204ee8) will decrease coverage by 0.62%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master       #2      +/-   ##
==========================================
- Coverage   64.18%   63.55%   -0.63%     
==========================================
  Files           3        3              
  Lines         215      236      +21     
  Branches        0       40      +40     
==========================================
+ Hits          138      150      +12     
  Misses         77       77              
- Partials        0        9       +9     

Flag	Coverage Δ
unittests	63.55% <100.00%> (-0.63%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
tests/unit/Token.py	78.57% <ø> (-3.58%)	⬇️
tests/unit/__init__.py	100.00% <ø> (ø)
pyTokenizer/__init__.py	61.35% <100.00%> (+0.06%)	⬆️

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