initial attempt.

// @sindresorhus @CWSpear 
Here's the only way I could figure out how to do this without explicitly accepting methods in the options, like `onPathInjected` and `onFileUpdated`.

The developer creates their own event emitter (anything with an `emit` method, really), and assigns their own listeners to it. The reason I had to go this way was because `wiredep()`, when executed with or without options, does everything all at once. e.g. there's no `var wiredep = require('wiredep')()` and `wiredep.run()`. The `.on('event')` listeners have to be configured before running `wiredep()`.

Should I scrap this, and just change the api to `wiredep = require('wiredep')()`, allowing `wiredep.on('event')`s to be bound before running `wiredep.run()`?