Format and lint

[alancleary]

• Adds linting via ESlint
• Adds formatting via Prettier
• ESlint and Prettier play nicely together using eslint-config-prettier
• Linting and formatting are applied to staged files on commit using Husky and lint-staged
• Linting and formatting are applied to PRs using a GitHub workflow

Edit:

• Linting and format was also applied to the existing source files