Use as NodeJS module

[leorossi]

To speed up process while working on #5 I realized that this tool may be useful also to be used as node module rather than CLI only.

I spotted a couple of issues that may be worth working on

• since UsedAssets is async, there is not way to know when Deadfile has finished his work, maybe extend EventEmitter and send events may be a solution?
• reporting is enabled by default, this means logging in console, on a file and starting a reporting server which parses the file. This should be optional and results of Deadfile's work can be stored in a variable

I'd like to use it like

const instance = new Deadfile(opts);
instance.on('end', (results) => {
    console.log(results) // console.log(instance.results)
   // do your own stuff with results of deadfile
});