[bug] set of control abastraction objects is incomplete

[DerekNonGeneric]

We are currently missing a couple of control abstraction object predicates from this library. This was in part due to there not being any documentation associated with them on MDN at the time when we published our initial round of package versions. Since then, along with a few of the good folks over at that project, I've gone ahead and wrote them up and we've gotten the missing pages added to the official JavaScript documentation.

Control abstractions can help to structure code, especially async code (without using deeply nested callbacks, for example).

• Promise: isPromise
• Generator: isGeneratorObject
• GeneratorFunction: isGeneratorFunction
• AsyncFunction: isAsyncFunction
• AsyncGenerator: isAsyncGeneratorObject
• AsyncGeneratorFunction: isAsyncGeneratorFunction