Add support for blacklisting rules

[macisamuele]

Fixes: #5

The goal of this PR is to add support for blacklisting rules via CLI parameters.
In order to achieve it we're using mutually exclusive CLI arguments, such that it would not be possible to have whitelist and blacklist defined at the same time.

[sjaensch]

Generally lg2m, fix tests and ship it. :)

[codecov]

Codecov Report

Merging #6 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master     #6   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          58     58           
  Lines        1724   1728    +4     
  Branches      104    104           
=====================================
+ Hits         1724   1728    +4

Impacted Files	Coverage Δ
tests/cli/run_test.py	100% <ø> (ø)	⬆️
swagger_spec_compatibility/cli/run.py	100% <100%> (ø)	⬆️
swagger_spec_compatibility/cli/common.py	100% <100%> (ø)	⬆️
swagger_spec_compatibility/cli/__init__.py	100% <100%> (ø)	⬆️
swagger_spec_compatibility/cli/explain.py	100% <100%> (ø)	⬆️
tests/cli/common_test.py	100% <100%> (ø)	⬆️

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