housekeeping

[MartijnR]

• use jsbeautifier config + tests, and exclude only engine.js and parser.peg => Replace this library #80
• use eslint and use separate passing config for engine.js perhaps
• convert tests to es6 => Replace this library #80
• run tests without having to create a bundle file, using karma-browserify
• convert tests so each looped test has its own it() statement => Replace this library #80
• complete and consistent JSDoc for custom functions