chore(ci): Migrate CI jobs to circleci

[rpl]

This pull requests includes the changes needed to migrate our CI jobs from Travis CI to CircleCI:

• new CircleCI workflow config (./circleci/config.yml), the workflow is organized as follows:

  • some notes about the CircleCI environment to set on the project (currently only NPM_TOKEN) and how to validate changes to the workflow file locally using the circleci command
  • references.nodejs_version is the set of nodejs version we run the tests on, these are the only properties of the workflow that needs to be updated to change the nodejs versions tested (without having to mess with the job definition and risk to break some by mistake)
  • a set of parametrized commands are used to reuse a set of steps in multiple jobs without duplicating too much stuff
  • a set of pre-configured jobs (one for the steps running on a linux container and one for the windows regression tests)
  • a predefined workflow with 5 job:
    • build-nodejs-current: run the full test suite (included additional steps for the functional tests), collect and publish coverage, persist build to reuse in release_tag job
  • build-nodejs-next and build-nodejs-experimental: run the full test suite, without flow-checks, coverage collection and running the functional tests only once in npm production mode
  • test-windows: run unit test and functional tests on windows (to catch windows-only regressions), skip flow-checks, coverage collection. This job does also retry once the functional tests if they fail (they used to be intermittent on travis windows workers)
  • release_tag: rebuild in production mode and release the new version on npm

• small changes to scripts used in CI jobs to adapt them to the CircleCI environment (in particular script/travis-pr-title-lint has been adapted to use the CIRCLE_PULL_REQUEST environment var).

  • NOTE: the project should be configured to only build pull requests, to make sure that the CIRCLE_PULL_REQUEST environment var will be set when the job does run for the first time on a github pull request (see https://support.circleci.com/hc/en-us/articles/360006357533--CIRCLE-PULL-REQUEST-is-missing-from-my-Pull-Request), this configuration should still make CircleCI to run the workflow on merges to master.

• migrated from coveralls to codecov (because coveralls would require a token which we can't expose to pull requests jobs)

Testing notes:

• the workflow file has been validated (and executed locally on docker to test the expected behaviors, besides the windows job)
• the release_tag job has been tested on a separate isolated test project, to double-check that the job does publish the npm package successfully as expected

[codecov-io]

Codecov Report

❗ No coverage uploaded for pull request base (master@335f0f1). Click here to learn what that means.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             master     #2096   +/-   ##
==========================================
  Coverage          ?   100.00%           
==========================================
  Files             ?        32           
  Lines             ?      1567           
  Branches          ?         0           
==========================================
  Hits              ?      1567           
  Misses            ?         0           
  Partials          ?         0           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 335f0f1...b591a71. Read the comment docs.

[rpl]

All the circleci jobs looks finally good now (included the windows one), it does submit the coverage data to codecov and I've just applied the last small "circleci"-related tweak to the script that lint the pull request message (which does make us sure that it does follows the conventions expected by the changelog generator utility when there is more than one commit in a repo9)

\o/

@muffinresearch @willdurand This should now be good to go, any additional review comments to cover before I'll merge this?

[willdurand]

r+wc

[muffinresearch]

Thanks for taking the time to get this up and running Luca 👍

[muffinresearch]

Good call on generalizing.