Add test case for descriptor with meta + payload functions

[nason]

Follow up to #199 (comment) and #200

@ztanner I added a test case here to make sure non-async and async functions were being handled in awaitWith. What do you think?

Seems ok here, but I'm thinking that it may be worth running the bundled code in lib through some tests too

[coveralls]

Coverage remained the same at 100.0% when pulling 004a7f3 on nason:awaitWithAsyncFnTest into 85aa8fb on agraboso:next.

[ztanner]

Yeah I think the underlying problem is that the bundler is expecting the awaited function to be async, since the transpiled code tries to then it. In reality, not everyone has an async payload/meta function, so this would throw.

I think it'd be a good idea to run the tests through the bundled code, because then I think we'd see some of these use-cases fail.