Await Event

A really stupid utility I use frequently for event emitters.
Allows you to yield an event and return the results.
I use this a lot of locking.

Note: you probably shouldn't use this for the error event.

Example

``js
var PassThrough = require('stream').PassThrough

var stream = new PassThrough()
// you attach it directly on an event emitter
stream.await = require('await-event')

co(function* () {
var chunk = yield stream.await('data')
var chunk = yield stream.await('data')
var chunk = yield stream.await('data')
}).catch(noop)

stream.write('some chunk')
`

You can use awaitEvent without attach on an event emitter:

`js
var EventEmitter = require('event')

var emitter = new EventEmitter()
co(function*() {
yield awaitEvent(emitter, 'ready')
}).catch(noop)
`

When use this for error event, it will reject once error event emitted:

`js
var EventEmitter = require('event')

var emitter = new EventEmitter()
co(function*() {
// it will throw when error event emitted
yield awaitEvent(emitter, 'error')
}).catch(err => console.error(err.stack))
``