add to work with async await module

[frani]

HI Shane, here is a resumen of changes:

• created module that work with async/await
• created module that test async/await module
• fix deprecated method
• fix variables name and replace 'var' for 'let'

[frani]

ups I see I was using different eslint config - I will fix later.

[sffc]

Thank you!

I changed my mind about backwards compatibility. I think we should bump the major version number and have async/await as the only API. If people can't use async/await, then they can use an older version of the library.

Can you please:

1. Undo all the unnecessary formatting changes. Most of this PR is formatting changes, not code changes, and it makes it very difficult to review.
2. Either remove the non-async/await code paths or make them wrap the old code paths (don't duplicate code).
3. Update the README file with new documentation.

[sffc]

To be clear, if you want to keep async/await in a separate namespace alongside the old-style code, that's fine. But, you shouldn't duplicate the code, as you appear to have done in this PR.

[sffc]

Please undo the name change of this file, or make sure it is similar enough to the old file that Git sees it as a file move. (Also for handler.test.js)

[sffc]

I'm closing this PR due to inactivity. Please reopen if you intend to continue with this change.