Add support for Codecov

[stevepeak]

Hey there,

I'm the founder of Codecov and would like to have an upload option for customers to send reports to Codecov.

Here is an example upload:

curl -X POST -d '<json>' \
    https://codecov.io/upload/v2?service=travis&branch=$TRAVIS_BRANCH&commit=$TRAVIS_COMMIT&build=$TRAVIS_JOB_NUMBER&pr=$TRAVIS_PULL_REQUEST&job=$TRAVIS_JOB_ID&slug=$TRAVIS_REPO_SLUG&tag=$TRAVIS_TAG

{
  "coverage": {
    "filename": [null, 1, 0, ...], //option-1
    "filename_2": {  //option-2
      "1": 1,
      "3": 0
    }
  }
}

Option 1 list of [line_number_coverage] index [0] is always null, index[1] is line one, etc.
Option 2 object of linenum: coverage

Full list of supported CI providers

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I'm happy to help our where I can!

Cheers,
Steve

[stevepeak]

Hey team! Checking in to see if we can get some help on this issue. Thank you 👍