Improve CI flow

[Taowyoo]

As @kwakkel1000 suggested, we need to add more check to the CI of this project.
Here are some points that we could add:

• Code Coverage: use cargo-tarpaulin
• Linting: use clippy
• Formatting: use rustfmt
• Miri: https://github.com/rust-lang/miri
• [Optional] Security Vulnerabilities: use cargo-audit

Here is some example CI piplines:

• GitHub Actions:
  • https://gist.github.com/LukeMathWalker/5ae1107432ce283310c3e601fac915f3
  • https://github.com/rust-lang/rust-analyzer/tree/master/.github/workflows
• Travis:
  • https://gist.github.com/LukeMathWalker/41c57a57a61c75cc8a9d137a8d41ec10

[Optional] I am also wondering if it's better to also replace Travis with GitHub Actions:

• developer will be able to run CI locally to check before push
• more tools could be used: build cache ...
• easier control of CI jobs: I cannot stop/cancel jobs in Travis
• more example CI setup we could reference since we do not have devops engineer for this repo : rust, rust-analyser ...

But these could be done in future, since it's not a must