New rule: no-async-without-await

[macklinu]

A follow up to the discussion in #78 (comment), it could be nice to have a rule like Ava's no-async-fn-without-await.

[alexilyaev]

Is this what you mean?
https://eslint.org/docs/rules/require-await

[SimenB]

Heh, yep! There's a difference between test code and application code though - in tests it's always safe to remove, but in application code, the API is changed (the function no longer implicitly returns a promise). But we might not need it here then, thoughts?

[SimenB]

People can use overrides to enable/disable the core rule for any files they want