Code cleanup

[victorlin]

Backlog of tasks, once other important updates are done:

• [x] use component.js+index.js [ref]
• [x] typescript + no semicolons + linting [ref]
• [x] use let/const over var
• [x] do away with export default [when it would be useful]
• [x] expand CONTRIBUTING.md with coding guidelines
• [x] consolidate result chart components (use latest implementation of SequenceChart+SequenceMatch)
• [ ] use function x() {} over const x = () => {} when not inline function
• [ ] settle on best way to assign objects on first render. either useRef or useState? useState with lazy init

  const chart = new SequenceChart("run-sequence-lookup-chart"); // doesn't work, will be reassigned on every render
  const chart = React.useRef(new SequenceChart("run-sequence-lookup-chart")).current;
  const [chart] = React.useState(() => new SequenceChart("run-sequence-lookup-chart"));

• [ ] use Tailwind's purge option [ref]

[lohrd]

useRef is a great way to accomplish your last bullet point above ^^^