Codecov Integration

[nickatnight]

Since this is a FOSS project, I propose adding Codecov integration (free). This will give developers who use this package a higher level of confidence when shipping code.

This can easily achieved by creating a workflow using GitHub actions adding codecov to after_success step in .travis.yml, which will run a coverage branch analysis on each PR. We can easily add a badge to the README and give full visibility of the project code coverage.

I can open up a PR

Note: this repo will need to be enabled via codecov dashboard