Integrate test code coverage reporting with Codecov and Travis.

[ghost]

resolves #18

• Install dependency
  • @istanbuljs/nyc-config-typescript
  • codecov
• Configure nyc to run test coverage
• Add scripts to run
  • test:coverage
  • codecov
• Configure travis to run test:coverage and codecov
• Add code coverage badge in README.md

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@3469291). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master      #19   +/-   ##
=========================================
  Coverage          ?   21.02%           
=========================================
  Files             ?       11           
  Lines             ?      176           
  Branches          ?       11           
=========================================
  Hits              ?       37           
  Misses            ?      137           
  Partials          ?        2

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[mesaugat]

@anishsilwal We only need to cover src files. Can you only include src files as part of the test coverage report.

Take a look here. leapfrogtechnology/async-store#23

[mesaugat]

@anishsilwal Also, require ts-node/register so that interfaces are also left out from code coverage. Same example above.