Migrate CI from Travis to GitHub Action

[mogeko]

Since June 15th, 2021, the building on travis-ci.org is ceased.

So I tried to migrate CI to GitHub Action. It can be better integrated with GitHub, especially for Pull Request.

I mainly wrote these workflows:

• build-test.yml: Run mix compile and mix test in different versions of Elixir and OTP
• benchmark.yml: Run benchmark tasks. It can only be started manually.
• release.yml: After adding tags to git, synchronously publish to hex.pm.

In addition, I need your help! 😃 @folz The workflow release.yml need add the HEX_API_KEY into the GitHub Action Secrets, It is only you can do this.

So, could you please help me to:

• Setup GitHub Action for this repository (if necessary) after you review the code I submitted.
• Generate a Key (with Write permissions) in our hex organization, then add it to GitHub Action Secrets and name it to HEX_API_KEY.

Thank u!

[folz]

@mogeko I added the API key to GH actions with that name. I'll let you merge this and verify it works, feel free to ping me if there's anything else I need to do.

[mogeko]

This is great! Thank you!