Implementing benchmark regression, fixes #13

[eullerborges]

• This implements a GitHub Action to track peformance benchmarks based on https://github.com/rhysd/github-action-benchmark.
• It'll warn Breno whenever there's a severe performance degradation caused by a push to master.
• I've tested this locally, the results can be seen here.
• For this to work properly, we need to create an empty gh-pages branch to hold the web page that'll allow tracking performance. The final result should become available under https://brenoguim.github.io/flexclass/dev/bench/. There's no way to open a pull request for a new branch in GitHub, which is unfortunate. To create the branch with an empty commit, it's possible to just:

  git checkout -b gh-pages
  git commit --allow-empty -m "Creating GitHub Pages branch"
  git push --set-upstream origin gh-pages

• It looks like there's a lot of variation on the resulting metrics. We'll need to evaluate whether tests should work over bigger samples.
• Note that there's no need to create a personal access token as proposed by the readme on github-action-benchmark. The bug reported in the community forums has been solved recently, I'm thinking of contributing a fix to that repo (they themselves are still using private keys).

[brenoguim]

Thanks for this contribution! The performance charts look awesome.

I created the gh-pages branch. Let's give this a try :)

It looks like there's a lot of variation on the resulting metrics. We'll need to evaluate whether tests should work over bigger samples.

I agree. I didn't write them with this infra in mind, so it's just a matter of tuning now I think.

[eullerborges]

My pleasure! I see that we now have a page properly working under https://brenoguim.github.io/flexclass/dev/bench/, now we can start thinking of other performance tests.