Drop Python 3.6 support

[pavdmyt]

Python 3.6 reached EOL: https://peps.python.org/pep-0494/

Plus some code reformat & applying new pylint suggestions.

[codecov-commenter]

Codecov Report

Merging #205 (93d5270) into master (2c46f9c) will not change coverage.
The diff coverage is 88.88%.

@@           Coverage Diff           @@
##           master     #205   +/-   ##
=======================================
  Coverage   97.79%   97.79%           
=======================================
  Files           7        7           
  Lines         363      363           
=======================================
  Hits          355      355           
  Misses          8        8           

Impacted Files	Coverage Δ
yaspin/core.py	97.49% <88.88%> (ø)

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