Promise interface for API

[leebenson]

recurly.api doesn't fit the Promise interface pattern of other calls - callback is currently required. Would be great to get this working per the other functions.

[umayr]

I had started to migrate the whole library to promises and drop support for callback but I couldn't get to finish that. I'll try to continue working on that.

[gus4no]

@leebenson I may be late for this, but if you want some sort of promise to work you can do a workaround like this.

await new Promise(resolve => { recurly.account.create(params, response => { resolve(response)}}

[englayth]

@umayr great work you have here, was wondering if you have finished promisifying the project or not ?
As Im using "recurly-js/promise" and when I see accounts.list has CallBack as first argument ...

[thgreasi]

@englayth try passing in a noop fn as the first argument and then the options object normally.
The results will be a promise in all cases, but we should definitely change the argument order in a major release.