[WIP] Adding code coverage & badge

[andrewwuan]

Reference:

• https://dev.to/j0nimost/using-codecov-with-travis-ci-pytest-cov-1dfj
• https://blog.travis-ci.com/2019-08-07-extensive-python-testing-on-travis-ci
• https://github.com/codecov/example-python/blob/master/README.rst

[raymondxyy]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@452b9b9). Click here to learn what that means. The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #29   +/-   ##
=========================================
  Coverage          ?   38.56%           
=========================================
  Files             ?       40           
  Lines             ?     3957           
  Branches          ?        0           
=========================================
  Hits              ?     1526           
  Misses            ?     2431           
  Partials          ?        0           

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[raymondxyy]

The bugs are because audlib/misc and samples/ are not bundled in the release. Can we do that?