Allow overriding Promise library

[NotBobTheBuilder]

Currently the when Promise library is hardcoded. A useful feature might be to allow overriding this when requiring, in case the implementer has a preference for another promise library.

For example, the pg-promise library achieves this with the pattern: require('pg-promise')({promiseLib: require('bluebird')})

[p-bakker]

Also an issue with the dependency on Bluebird, as Bluebird doesn't support async_hooks in NodeJS, which results in amqplib not supporting async_hooks

[xenoterracide]

really want this so we only need native promises, would a PR make it happen?

[Worthaboutapig]

I've done this and created a PR, though with a few caveats which shouldn't be a problem for most: #599

[cressie176]

I'm going to close this in favour of just using native promises #627.

Thanks for the PR @Worthaboutapig, and sorry it didn't get reviewed. I took a quick look just now and it includes a few unrelated changes (typescript defs, linting, plus maybe some dependency bumps), so I wouldn't want to merge. It will be useful as a reference point though.