Simple proposal for enabling promises

[acoll]

Fixes #523 (it's a good idea to open an issue first for discussion)

• npm test succeeds
• Pull request has been squashed into 1 commit
• I did NOT manually make changes to anything in apis/
• Code coverage does not decrease (if any source code was changed)
• Appropriate JSDoc comments were updated in source code (if applicable)
• Appropriate changes to readme/docs are included in PR

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CLAs look good, thanks!

[JustinBeckwith]

Thank you for the PR! It turned out to be a little more complicated, due to the desire to have proper TypeScript typing. I really appreciate the nudge, and it led to us submitting #1091, which shipped in 28. Thank you again!

[acoll]

Awesome. Thanks for your work on it, I'll be updating today and removing my promisify wrappers. Thanks again.