Add CircleCI config

[andreypopp]

This adds CircleCI config, this repo still needs to be added to CircleCI.

What CirlceCI does with this config:

• installs esy
• installs & builds reason-cli
• produces npm release
• installs it and tests
• uploads artifacts

Artifacts can be fetched either manually from CircleCI dashboard or using this guide.

[jordwalke]

Thank you, @andreypopp