Use GitHub Actions for CI

[rhysd]

Hi,

I found that CI has failed for a long time.

I replaced CI of this repository with GitHub Actions.

Pros are:

• Anyone who has an account on GitHub can access the results. (CircleCI requires their account to see the results)
• Variations of Windows/macOS/Linux workers can run with one workflow

I configured a new minimal workflow which runs on macOS/Windows/Linux with Rust toolchain stable and 1.36 (MSRV of this project).

And I confirmed all tests passed with my forked repository: https://github.com/rhysd/term-crate/actions/runs/1368569222

[rhysd]

New workflow ran successfully on the merge commit. Would you disable CircleCI for this repository?

[Stebalien]

Already done :smile:.