Add ESLint, Prettier, auto-changelog #41

Following our other libraries, we should lint and format this project with ESLint/Prettier.

• Add our ESLint packages as dev dependencies (minus TypeScript and Jest)
• Add ESLint configuration file
• Add Prettier as dev dependencies
• Add Prettier configuration file
• Add @metamask/auto-changelog as dev dependency
• Fix any lint violations with changelog (also see Add links to the CHANGELOG #51)
• Add lint and lint:* package scripts