Adding in the ability to serve static resources

This is allows you to serve up static resources using the same server that browser-run is using.

### example usage

```javascript
var run = require( '../' );

var browser = run( {
    static: true
} );
browser.pipe( process.stdout );
browser.write(
    'var img = document.createElement( \'img\' ); ' + 
    'img.onload = function(){ console.log( \'img loaded\' )}; ' +
    'img.onerror = function( err ){ console.log( \'img errored\', err )}; ' +  
    'img.src = \'./examples/foo.png\'; ' +
    'document.body.appendChild( img );' 
);
browser.end();
```

If the resource is there then it will log "image loaded"

Also I was thinking on how we could test this let me know if you have any ideas

once this is merged I think I can have a pr ready for `tape-run` to be able to pass this flag.