ban var (and more new rules)

1. no-var: obvious
2. require-await: we usually don't want to have an async function that does not await
   • Sadly, we cannot catch with eslint where we call an async function and we don't await, I'd really like that, too.
3. (updated) no-unused-vars: we usually don't want unused parameters (semistandard doesn't seem to catch that)
4. (updated) no-restricted-syntax SequenceExpression: we don't usually use the comma operator and sequence expressions; inexperienced programmers coming from other languages can use it by mistake, thinking it does something else