Support for Async Iterators/Generators syntax

[michaelsbradleyjr]

Async Iterators/Generators are at Stage 3: https://github.com/tc39/proposal-async-iteration

Great stuff, really! js2-mode complains about for-await-of, and also async generators when given as methods on a class.

[brn]

+1

[bellbind]

+1

"Aync generator" function/method and "for-await-of" loop are now in released ECMAScript-2018.

• https://www.ecma-international.org/ecma-262/9.0/index.html#sec-async-generator-function-definitions
• https://www.ecma-international.org/ecma-262/9.0/index.html#sec-for-in-and-for-of-statements