Move all CI / CD to github actions

[damithc]

There is a change to Travis pricing model https://blog.travis-ci.com/2020-11-02-travis-ci-new-billing
We should explore alternatives e.g., GitHub Actions

[ang-zeyu]

Remaining:

• appveyor
• docs deployment (see travis.yml)

[tlylt]

Remaining:

• appveyor

Currently we run tests on every PR via Appveyor and Github Actions, do you mean we should remove the Appveyor check since Github Actions script now runs the test as well.

If that's the case, I guess the course of action:

• remove appveyor.yml in root directory
• terminate the CI on Appveyor platform
• update ci.yml to run test on both Ubuntu, Windows & MacOS

[jonahtanjz]

Currently we run tests on every PR via Appveyor and Github Actions, do you mean we should remove the Appveyor check since Github Actions script now runs the test as well.

@tlylt I believe they are running the same tests but the difference is that Appveyor is running the tests on a Windows environment and the current Github Actions is using an Ubuntu environment. Since Github Actions also supports Windows environment, we should also include the Windows environment tests on our Github Actions and remove the one on Appveyor.