Add code coverage

[RichardLitt]

See ipfs/kubo#3053 (comment).

[harlantwood]

+1

[Kubuxu]

We use currently two coverage report providers, coveralls and codecov. Many of our current repos (especialy js) use coveralls but codecov has superior UX and UI, transition would be trival.

[RichardLitt]

@Kubuxu Cool. What should I add? The badge?

[Kubuxu]

I think it badge which links to the project's page would be ok.

[RichardLitt]

Cool. And that is for all go-* and js-* repos, right?

[Kubuxu]

Not all of them have coverage reports yet but yes.

[RichardLitt]

Ok. Can you point to one example of the badge? I'm not seeing it on go-ipfs; is it being used elsewhere atm?

[RichardLitt]

Or is this it:

[![Coverage Status](https://coveralls.io/repos/github/ipfs/go-ipld-node/badge.svg?branch=master)](https://coveralls.io/github/ipfs/go-ipld-node?branch=master)
[![Codecov](https://img.shields.io/codecov/c/github/codecov/example-python.svg)]()

I'll add the second (codecov) and open an issue about switching; that work for you? Where should I point questions about that - I don't see an issue in ipfs/community about the switch. Where is that discussion happening?

[Kubuxu]

There was no discussion yet, I will start issue in community.

[Kubuxu]

I like this style of badges a lot:

We could use the same style of icons from shields.io for Travis, Circle and the normal task:

[RichardLitt]

In that case, I will start looking for or adding:

![CodeCov](https://img.shields.io/codecov/c/github/ipfs/go-ipfs.svg?style=flat-square)
[![Travis CI](https://travis-ci.org/ipfs/go-ipld-node.svg?branch=master)](https://img.shields.io/travis/ipfs/go-ipld-node.svg)

To every IPFS repo.

[Kubuxu]

We should probably make the coverage shield clickable.

[RichardLitt]

[![codecov.io](https://img.shields.io/codecov/c/github/ipfs/go-ipfs.svg?style=flat-square&branch=master)](https://codecov.io/github/ipfs/go-ipfs?branch=master)
[![Travis CI](https://img.shields.io/travis/ipfs/go-ipld-node.svg?branch=master&style=flat-square)](https://travis-ci.org/ipfs/go-ipld-node/)

Look better?