Adding initial promise end point

[jung-kim]

fix: #15

WIP

• Adding in package-lock.json per article at here.
• Adding in Semaphore.waitAsync() that returns a promise
• Adding in test. (Added random ness to the next tick to introduce some randomness in call order)

(will add implementations and tests to others when current impl is deemed acceptable)

[ronkorving]

I'm not sure if I'm a total fan of postfixing all API with Async. In #15 I asked and was hoping you would have a few suggestions regarding what we could do here. I guess this PR is one suggestion :) Did you have any other ideas? I have some, but don't mind hearing your thoughts first.

[jung-kim]

Yeah, sorry I'm bit shit at describing my thoughts and figured code is the best way. I don't mind evolving or scrapping this PR.

As fars as Async postfix, yes I do find it very strange and I'm not a fan of it myself. However, I'm not aware of any standards around this but Bluebird's promisify all function follows this convention and it is the only one that I'm aware that does this.

I personally would have preferred to called it ${function_name}Prom() format

[ronkorving]

Myself, I was thinking it may be nice to be able to get a promisified version of locks by calling:

const locks = require('locks/promise');

Or something like that. That's just one alternative, there may be more :)

[jung-kim]

Been quite busy meself, and it is now fixed.

And Yeah, I would agree that doing such sub directory is a better idea. I've tried to reutilize existing logic so plea feel free to let me know.