Test code coverage

[Lercerss]

Coverage using Codecov and coverage.py for #83

• Added integration of Codecov to the repo.
• Added codecov and coverage.py to requirements
• Added coverage pill to readme
• Initialized coverage.py config to generate reports only on project specific files.

Reports are available under the codecov repo's page (overview is empty for now since not implemented on master).

[codecov-io]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@814b67b). Click here to learn what that means. The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #90   +/-   ##
=========================================
  Coverage          ?   74.14%           
=========================================
  Files             ?        5           
  Lines             ?      352           
  Branches          ?       45           
=========================================
  Hits              ?      261           
  Misses            ?       70           
  Partials          ?       21

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Continue to review full report at Codecov.

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