Promise support

[christav]

Implements #2.

Added transparent support for promise returning functions.
Added ambi.promise as a hook so that the promise implementation used can be replaced if desired.
Updated docs.

Hopefully I didn't break the automation; I'm working on Windows and a bunch of the NPM scripts don't work there, and I felt that fixing that problem (if you want to) is better in a separate PR.

[balupton]

Will need to be a major version change, as it makes the minimum node version now 0.12 instead of 0.8. I can do this. Which is why the CI tests failed.

If you are ok with this, can we dump the custom promise library support? People can just do customPromiseLibrary.resolve(ambi(…)) or ambi(…).then(customPromiseLibrary.resolve()) to convert it.

Otherwise, LGTM, excited to get this in there.

[christav]

The custom library support is only necessary for supporting old environments (like Node 0.8 or really old browsers) that don't have a native promise implementation. If you're happy cutting that support then sure, happy to take it out.

[balupton]

The custom library support is only necessary for supporting old environments (like Node 0.8 or really old browsers) that don't have a native promise implementation. If you're happy cutting that support then sure, happy to take it out. ...

@christav great, let's cut it. People can just use polyfills in that case anyway.

_{Sent with GitHawk}

[christav]

Hang on a sec, I think there's a fundamental misunderstanding on my part. I thought the whole purpose of this library was to consolidate the various sync and async calling patterns in to a single callback-based one. The example you specified above is predicated on ambi returning a promise, which my code does not do - and neither does yours for sync or async cases pre-PR. In fact I updated the docs because the ambi function explicitly returns null, not a value, so the docs didn't match the code. See index.js, line 97 for the code in question.

So I'm a little confused as to what you want the API to be here? In the meantime I'll take out the custom promise support in the meantime while we figure out the right api.

[balupton]

I thought the whole purpose of this library was to consolidate the various sync and async calling patterns in to a single callback-based one.

Sorry for the confusion. That is correct. This does not need to return a promise.

Returning a promise can come in a later major version of ambi/taskgroup/kava/event-emitter-grouped, as it would require major additional changes to all of them, such as await ambi(…), await task.run(…), await taskgroup.run(…), await suite(…), await eeg.emitSerial(…).

Right now the biggest value we are wanting is to return promises to tasks/tests, which is what this PR will enable.

[christav]

Updated PR, build is green. @balupton we good to merge?

[balupton]

Will merge, and then will work on promise returns, as that seems to make most sense considering its API.

[balupton]

Released to v4