GH-46: Add flake8 config

[didix21]

• Format mdutils source files.
• Format mdutils tests files.

[codecov]

Codecov Report

Merging #86 (75f7b29) into master (f4562f9) will decrease coverage by 0.03%.
The diff coverage is 82.20%.

❗ Current head 75f7b29 differs from pull request most recent head 73767f5. Consider uploading reports for the commit 73767f5 to get more accurate results

@@            Coverage Diff             @@
##           master      #86      +/-   ##
==========================================
- Coverage   88.37%   88.35%   -0.03%     
==========================================
  Files          13       13              
  Lines         499      498       -1     
  Branches       95       95              
==========================================
- Hits          441      440       -1     
  Misses         37       37              
  Partials       21       21              

Impacted Files	Coverage Δ
mdutils/mdutils.py	74.60% <70.00%> (ø)
mdutils/tools/Header.py	82.35% <71.87%> (ø)
mdutils/tools/TableOfContents.py	88.88% <80.00%> (ø)
mdutils/tools/TextUtils.py	91.48% <80.95%> (ø)
mdutils/tools/Table.py	90.24% <86.66%> (ø)
mdutils/fileutils/fileutils.py	100.00% <100.00%> (ø)
mdutils/tools/Html.py	93.87% <100.00%> (ø)
mdutils/tools/Image.py	100.00% <100.00%> (ø)
mdutils/tools/Link.py	97.36% <100.00%> (ø)
mdutils/tools/MDList.py	100.00% <100.00%> (ø)

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