Linting fixes, npm scripts

[laurence-myers]

• package.json:
  • Add npm script check:lint to lint all files per each tsconfig
  • Add npm script check:tsc to type check all files per each tsconfig
  • Add npm script check to run both check:tsc and check:lint
  • Specify engines, NodeJS v14.
• Auto-fix many linting issues
• Manually fix some linting issues
  • Rename shadowed variables
  • Replace eval() when calculating frame rate, with string split & explicit division
• Disable linting for some warnings.
• .gitignore: Ignore /.idea, added by IntelliJ IDEA

I tried adding a new Workflow to execute check, but it failed to install fsevents. I don't know how to fix this using npm, I suggest replacing npm and package-lock.json with yarn and yarn.lock, which behaves better across different systems.

Failing CI step

[whyboris]

Thank you for the contribution! I'll try to find time in the near future to test-drive it 😉 merge this in 🤝

[whyboris]

I'm loving this 😍
Thank you very much!

[whyboris]

Awesome 🎉
Thank you 🙇
So good 🤩